"My problem involves my 14-month-old son," writes an Alexandria mother. She and her husband are both 30 and he is their "first and only child":

"Tommy has never slept through the night. My doctor's only advice is 'Let him cry.' However, at age 9 months, he climbed on the bumpers and fell out of his crib while crying at 2 a.m. The bumpers are gone, but I'm afraid he could still climb out. If we don't give him bottles of juice he cries and cries until we give in. This happens at least three times a night. Please help!!"

A. There are quite a few things we would do, but the first would be this: Quit giving Tommy any juice at night. You still can give him TLC with a bottle of water (although he won't like it as much), and he will be healthier for it. Any more than four ounces of juice a day gives a child so many calories he might not eat all the foods and roughage he requires.Besides, anything but water at night will coat his teeth and could cause bad cavities.

And then there is one more thing we would do: Get a second opinion. You might even consider changing pediatricians.

A doctor who tells you to let your child cry is about as helpful as a plumber who tells you to let your faucet drip. We can't believe Tommy wants to cry, any more than you would, and when he does, he has the right to be comforted. It isn't natural for a child to cry; it's just the only way he can tell you that something hurts.

That "something" could be psychological, it could be metabolic, it could be alle-gic -- it could be all sorts of things, and to find out, Tommy needs a doctor who will take a long case history, give a thorough exam and maybe some tests to rule out hypoglycemia, dehydration or other problems. He also needs a thorough study of his diet.

The newest medical thinking contends that an allergy should be explored whenever symptoms are chronic, even though they are as diverse as a stuffy nose (or a runny one); headaches; itching eyes and ears; minor hearing or visual difficulties; earaches; sore throats; tonsillitis; asthma; nausea; stomach aches; diarrhea; constipation; frequency of urination; urinary infections; sore joints; dizziness; hives; gas; rashes; eczema; drowsiness; anxiety; hyperactivity; depression; sudden anger; fatigue and many other seemingly unconnected symptoms.

Dr. Benjamin Feingold, with his hyperactivity thesis, is a pioneer thinker in this field, but Marshall Mandell, certified by the American Board of Pediatrics and Pediatric Allergy and a consultant to the Gesell Institute for Child Development (and at odds with many of his colleagues), goes much, much further.

His new book, "Dr. Mandell's Five-Day Allergy Relief System," which he wrote with Lynne Waller Scanlon (Crowell; $9.95), is bound to be as controversial as it is provocative. While we are in no position to endorse either a medical theory or a treatment, we think you'll be interested in reading abou the physical and mental reactions he claims different smells and food can cause.

To Dr. Mandell, it is only reasonable to believe that a child's early introduction to foods; to cow's milk and to the diversified diet of this century, as well as to air pollutants and herbicides, are sure to trigger sensitivities. People, he says, just can't evolve that fast.

It takes a doctor to make a diagnosis, but sometimes parents can play detective with great skill, for no one else cares so much.

Start by asking yourselves: When did this crying get worse? Has it always been this way? Then make a calendar in retrospect. Record everything that could have affected his sleeping pattern, from the scares at night to the sitter who made him cry so much, to the strange rash he got at the beach. Nothing is too fanciful to be included.

Also note when anything new was introduced in his room: a new kitten, maybe, that would shed dander, a kapok mattress, a wool blanket, or some potted plant with mildew in the soil? List all the foods he has been eating, including the additives and preservatives listed on the jars, and when they were started.

Now bring the calendar up to date with an hour-by-hour chart of his behavior; his food; his bowel movements; the hours he sleeps and whether he was in the house or outdoors, so the doctor might find a correlation.

You also can do some testing. See if the problem is in his room by moving the crib into the living room. If the mattress or the blanket might be bad for him, lay him on the floor on a comforter in another room, boxed in with pillows, after he's gone to sleep. What about the detergent? Switch to a mild soap and run the clothes through the rinse cycle at least one extra time.

Your doctor may have you begin testing for food allergies, by removing one food at a time from his diet for five days, which is how long it takes the body to get rid of a reaction. Simply quitting the juice may be enough. If that doesn't work, Tommy may be taken off wheat, for example, or milk -- the worst offender of all. For this, all dairy products are stopped, including cola drinks, caramel, and anything else that contains milk sugar (lactose).

Other doctors use other methods, but if you're still breast feeding, all doctors will require that you quit any food you take out of your baby's diet, since your own milk will carry the allergens.

There's one thing about these home allergy tests: They don't cost anything, they won't hurt Tommy, and at least you'll feel like you're doing something about the problem while waiting for the doctor to discover what it is -- with or without your help.