Yeah, I'd definitely love to know which breeder you got him from. Did she tell you exactly what it is you're giving him?
I would take him to the vet for a real assessment. I don't want to call any names, but my hogs have been HEAVILY infested with mites before (they got brought in when I bought a new girl - more like rescued!). They never got lumps. And trust me, you would know, because they don't just bite them, they'll also bite you. I remember well, because they infested the whole house and there were bite marks all over us. And the only thing that can cure mites is a trip to the vet and some worming shots, along with complete bedding changes and cage disinfection, as well as thoroughly vacuuming all the carpeted/upholstered surfaces.
If you can't get small bags of the royal canin baby cat 36, I believe it also comes in wet food form. And if he doesn't like to eat anything else, he should really enjoy that
It's what I fed my baby Raphael when he was dying from testicular cancer. I'd also closely watch him, make sure he acts normal, as well as watch his stools.
You're welcome. I'll be keeping my fingers crossed for you and your little man!