Weight Gain!

My whole life I was small, I still feel very small now. Throughout all of high school I weighed 100-109, never over never less. My first year of college as well. Now I'm going on 20 years old and 5'2 going on 129.5lbs! I use to complain about not being able to gain weight but now I'm packing it on like nothing! People say I don't look as if I've gained much weight and I don't look bad at all but I was wondering , because of my height am I considered over weight , under, or just about right?