Please help!!

I just recently bought a chin from a friend who could no longer have him in her apartment. He was super cuddly and great around her kids. Now that he's been here, he will not let me pick him up, and the past few days when I stick my hand in the cage he nips at me and won't even let me pet him. Instead he jumps all over the cage so that I can't pet him. I let him out of the cage for over an hour a day, just to run around in a room. Last night he started barking at me while I was trying to lure him back into his cage. He's almost 3 years old. Why is he acting like this?? I want to be able to hold him without him nipping at my boyfriend or I! Someone please help!