I agree with the other posters about taking him to the vet but I have a thought as to what might be happening if all the vet tests come out ok. I don't know if your male is neutered or not but sometimes there can be pretty vicious fighting among males over territory. To the point where one cat is eventually driven away from the area or in rare cases even killed. A few years ago I had the opportunity to observe a feral colony on a daily basis and once the male kittens got to a certain age the dominant male of the colony fought them and ran them off and I never seen them again. Could it be possible that your cat is in this kind of situation??? I definately wouldn't force him to go outside just in case. Something is causing him to seek the safety of home. Hope whatever the issue is gets resolved!! ;-)
Hi, I totally agree with Opus that kitty really needs to see a vet. The meowing constantly doesn't sound typical for your kitty, and he could be in pain. He's a young male, and sometimes they get urinary blockages that are painful and can be very serious. I'm not saying this is what it is, but it might be.
Please get kitty to the vet ASAP.
Have you considered taking your kitty to a Vet?...usually constant meowing is a good sign of pain or something really bothering kitty, I think you really need to have him in for a good check up....please!