Infection 3 weeks after Neuter?

I just adopted a dog that was neutered on the 16th of last month.  I thought he might have fleas as he was biting and licking his back end very intensely.  When I looked last week he had a scab over his stitches but recently after the biting, I noticed the area has swollen.  

Advice?

[Margot49]

Contact the agency you adopted him from, tell them and say you want a Vet to check it.  There should be no charge to you.