Has ANYTHING at all changed in the house around the time this behaviour started? Even if furniture got moved and he lost a favourite hiding place or something, this can cause it.

Also - even though he got a clean bill of health in February, another checkup wouldn't hurt. A tooth may have gotten sore, he may have a UTI that is bothering him and making him grumpy. Ill health can do that.

I'd say vet check first.

Then- I don't know how you feel about these things - but there is a wonderful pet psychic on here that many have used with great success.

Best of luck - I am sure your sweet boy will be back soon!