extra skin/flab even though i exercised and dieted for 4 months

[bovinus]

hey guys i'm pretty new to fitness and whatnot but i spent my entire summer lifting weights every other day with my friend. i am 6'2 and weigh 150 now (lost about 15 lbs) and didn't gain much muscle other than biceps. i am pretty thin but my mid-section (belly, sides, and lower back) are loose still. i can grab my lower back with two hands and i don't think it is fat. i used to be very overweight a few years ago (210 lbs as a 15 year old). i am 18 years old now and any advice/tips/explanations would be greatly appreciated.