Hello and thank you for asking your question on just answer. My name isXXXXX will try to help.
1. Is he still having diarrhea?
2. Is the skin, in the swollen area, red?
3. How much does he weigh? I can give you some over the counter things to try.
Is it a soft "balloon" type swelling? Can you push the swelling in and make it go away until it pops back out?And the skin is normal? Is he neutered?
Or does it seem to be more like inflammed skin?