My Six Year Old Min-pin Is Acting Very Odd.he Seems To Be Very Sensitive To Anyone Bumping Into Him, Or Picking Him Up. He Does'nt Seem To Be Himself . His Appetite Seems Good, What Could Be Wrong?

I don't know why but he just seems to be whiny and clingy lately. He has fleas and i have advantix for him but don't want to apply it if he's ill. He has a lump on each side just in front of his rear legs on his back, but i'm not sure if that is a muscle or what? He runs and jumps just fine. We have added another puppy to the family lately.[a catahoula] and the min pin does'nt really like him all that much. Can you please help us out