Bei Bei, a giant panda at the National Zoo, had a stomachache. But zookeepers figured something more was going on.

He had several other concerning symptoms — nausea, not much of an appetite and lack of sleep. They figured it might be a mucous stool. And after a thorough vet exam, their diagnosis turned out to be right.

Bei Bei “passed a mucous stool” Sunday and had started “eating and defecating normally again,” according to the zoo. But then it appeared as if he didn’t feel well again Monday.

He didn’t want to go outside and seemed “reluctant to eat,” officials said.

Bei Bei, the Smithsonian National Zoo's giant panda, celebrated his second birthday with cake Aug. 22. (Reuters)

Bei Bei is 2 years old.

Zookeepers watched him closely Monday night and did a full veterinary exam Tuesday. Blood and urine samples were taken, according to the zoo, and he got a full exam of his stomach and colon with an endoscope camera.

Officials said that the exam went well and that they “found evidence of a mucous stool but not an intestinal blockage.” Some bacteria in his urine suggested that he may have a urinary tract infection.

For giant pandas, mucous stools are not uncommon. Officials at the zoo said that Bei Bei has passed several of them and that Tian Tian and Mei Xiang — two other giant pandas — also get them occasionally.

On Wednesday, Bei Bei was “bright and alert,” the zoo said, and had recovered from his exam. For his recovery, he was offered small amounts of bamboo and honey water.

Keepers said he was getting back to his “normal routine and spending time outside.”

“He settled in for a morning nap in his preferred tree,” zoo officials said in a statement.

Bei Bei will get smaller meals over the next few days, officials said, as he continues to recover.