Congrats. We waited forever for Hot Rod to gain weight. He was 1.5 lbs when we got him at 15/16 weeks. I kept taking him to the vet to weigh and it took probably 2 mos before he got to 2 lbs!
He was just under 3 lbs at 6 1/2 mos when he got neutered. As a matter of fact, I was looking at his the very first piece of clothing (a parka coat) that we bought him and it doesn't even go around my fist. lol. It was slightly big on him. He is was 3.7 lbs yesterday for his annual vet visit.
You should be able to drop in at the vet to weigh your baby. My vets all were just as excited as I was to see how big each were getting.