Tucker was 5 pounds even at 4.5 months old, he is now 9 pounds and has hasnt gotten any bigger since he was around 7/8 months, on the 23rd of this month he will be 10 months old. He got bigger than I expected being that his parents were around 4 pounds each, however I LOVE his size, he is still small (7 inches in height) and solid as a rock, he is not fat at all. I certianly worry less about him than I do my 4 pound toy poodle (2.5 years old). When I look into getting another dog I will definitly will look into one that is going to be on the "bigger" side.
Your pup will probably be around 10 pounds when fully grown and that is still a small dog, more to love!!