Wet tail is a very serious disease caused by a bacteria which infects the bowel. It causes the bowel to really just give up working and the hamster cannot digest food. It has a very distinctive odour and to be honest I don't like the sound of your little guys tummy. Is he still active and bright eyed or does he seem to be walking sort of hunched up and miserable. Wet tail usually gives messy diaorrheoa all over the underside. The ham cannot control this or has the energy to clean itself. Stress on moving o a new home can bring it on as young hamsters have immature systems.
Look here for more info:
http://www.hamstercentral.com/wiki/Wet_ ... ve_Ileitis
I hope it is just too much veg and fruit and he is well soon.
He is young and needs time to settle and tame. If he gets worse he must see a vet. P@H often have 7 day surgeries in their stores if you need one quick.