When you say diahorrea, how often/colour? Cos i think mouse may have something similar, he has frequent periods of quite liquidy poos which we haven't as yet been able to link to any specific foods.
When he has it I'm sure it's not an actual bug type diahorrea, when he had a bug he did lots of nappies and the contents were sort of watery and green; what i'm talking about is more back along the spectrum towards baby poos and max 2 in a day.
It's one of a few things putting us off trying potty training as yet. No help to you i realise, but will be interested to see what you find out. If we ever get around to having his 2-3 yr check i was going to ask the HV about it.
Mum to Mouse b May 2009 & Little Hamster b Feb 2012.