Have 2 year old cats. Both are spayed and neutered and belong to the same litter. They were buddies but sometimes fought, mostly out of fun. In a last few days, the male cat is looking for opportunities to chase and jump over the female cat and bite her. She hisses back and I have to clap my hands to scare him away. This is becoming more frequent. They had their vet visit 3 weeks ago and everything was well. They took rabies and distempering shots.
What could be wrong with the male cat?