I have a year old male cat - he is normally quite an independent cat, but very affectionate. I moved house 6 months ago, and he seemed to settle in well.
The past week he has been doing some really weird things - meowing REALLY loudly (he is part siamese, so I am used to pretty loud and persistent meowing but this is 4/5 times worse than normal) and constantly, day and night, he is constantly hungry, no matter how much I feed him, he has started spraying (he isn't neutured, and I'm not sure if this is natural or a symptom of the problem at hand), and this morning he totally freaked me out - he has been mewing constantly since about 6 this morning, and nothing I do makes any difference - normally he'll jump onto my lap, purr a bit and then fall asleep, but today, he won't let me near him, and basically I thought perhaps he needed some "safe space" on his own, so closed all the doors and left him in "his place". A little while after I'd done this, his mewing got worse so I went to him and found him literally trying to climb the walls - my bedroom door has a window thing at the top, and he had managed to climb up to this and was clinging on - as soon as he saw me he jumped down and ran away. I've made sure he has food, water and a clean litter tray, but he is starting to really worry me - vets say nothing is wrong but there is something wrong with him - he is being aggressive to me which has never happened before! Someone please help! Worried sick and don't know what to do for him

Definitely not being neutered is part of this problem. Male cats that are not neutered before 6-8 months of age will usually start spraying.As for the constant meowing, and this is just a thought, is there any possibility there could be a female cat in heat roaming around your house? It just seems like a bit of a coincidence. And animals will act very strange in that situation.

Quite personally, I don't consider an unneutered male cat to even be a pet. They basically want one thing. They'll start spraying, they usually want outside pretty badly (and I hope you're not letting him out to make more strays), and yup, any time a female is around they'll react, especially one in heat!

I can't believe the vet didn't say something about this. That's a bit ignorant for a vet.

Even if there's another problem, get him neutered anyway. And it might solve the problem as well.