Could be, or maybe he is just the runt of the littler, every litter has one. I used to breed my yorkshire terriers and they had a total of 6 puppies, there was ALWAYS a runt who matured slower than the others and one who was the alpha animal of the litter who ate the most and grew the fastest.

If you want to avoid that then youre going to have to lock the cat in your bathroom while you are out. If not that then youre going to have to buy some of those female cat "heat" underwear that they have around to keep him from spraying. If you dont like any of these ideas I dont think there is really much else you can do unless you want to drown him.