Yep unfortuately 3 years is about the life span. Our hampster recently died and had some of those symptoms. I noticed a bump on her neck too. Cancer is a real possibility with rodents of all kinds. You best have you little one checked. I tried things like a food change too and she seemed some better for a while but ... Well you know the rest. I hope you find out that it's nothing and he's just bored with his diet. Good luck!