Kitten with sore bottom

Question
Hi, I hope you might be able to put my mind at rest.  9 days ago i witnessed a kitten being dumped on the road by the driver of a car.  I took it to vet immediately, because I wanted to keep him, and the vet treated it for worms and fleas.  He said it was 4 months old, but I am wondering if it is younger seeing as it still as the baby teeth.

When the vet tried to take his temperature, he really hollered.  His anus often bulges and looks sore sometimes.  His motions are on the loose side, bit belly is a bit swollen. He has flatulence.  He is eating dry kitten food.  He is lively and eats well.  But he is obviously experiencing discomfort in his rectal area.

We are returning to the vet tomorrow for him to have his inoculations.   I am hoping his problem is purely caused by change of diet.  I live in Turkey and its likely his diet was very bad before we took him in, and he may have been on bread and water (I live in Turkey), or cow's milk.

We go to the best vet in this area, but sometimes I feel they are not trained as well as they are in the UK.  I am hoping you might be able to suggest what this little chaps problem might be, before I take him to see the vet, because I am worried something has been overlooked.  I never felt I had to question my Vet in the UK, but here is so different.  Sorry if this sounds bad.  If I knew of another Vet in this area that was better, I would certainly go to him.  *sigh*

Answer
You should have the vet re-test the kitten's stool looking for other parasites like coccidia.  These can cause straining to have a bowel movement and that can cause the rectum to bulge out.  As far as the age, we usually say that a 1.5 kg to 2 kg kitten is around 4 months of age.