Diarrhea for 3 weeks in 2.5 year old

Wondering if anyone has had the same experience with their child. My 2.5 year old boy has had diarrhea for 3 weeks now. He vomited the first day but that was it for barf. No fever. Very good appetite. Tired, he even naps at daycare, something he rarelly does in normal times. Generally he is in a very good mood, not much crankiness.

But the diarrhea will not go away. He was tested for several bacteria strains: all negative.

Can it be a virus? Which one? At daycare, they keep telling us that no other kid has diarrhea, only him... Weird!

[RockRose]

Since he had the first bout of diarrhea,  have you kept him on a restricted diet?    I had a similar thing happen with one of my boys and it was diagnosed as "starvation diarrhea" (not that he was literally starving,  but he was limited to the BRAT diet).  Is he eating a normal amount and variety of foods?

[Ecologic]

Thanks for your answer, he was partially on the BRAT diet, he has been back on his regular diet for a few days now.

We think we figured out why he had diarrhea, not even sure there was ever a virus. He has been going through a growth spurt for a month. He takes pancreatic enzymes for his deficient pancreas but now he was not taking enough anymore. We increased the dose and the number of stools per day has been going down. Bouts of diarrhea are bound to happen until he becomes an adult, not fun.