(Question about weightlifting)?

I just turned 16 a week ago, I'm about 5'10," and weigh about 125 lbs. (Yes, I realize how thin I am). I've been weightlifting since around April of 2009 off and on but mostly on and I just haven't really seen the results I had imagined. I'm forced to use the dumbbells at home (unless I can go to the gym which isn't that often) and as of right now my routine is: bicep curl 3x16 (8 curls for each arm) with 30 lb. dumbbells (like I said above, I don't have anything but dumbbells at home), hammer curl 3x16 (again, 8 curls for each arm) with 30 pounders, and then I dumbbell (bench) press 3x10 with 40 pounders. After I've done those three things, I do 3x25 stomach curls and two push-up burnouts. I just started doing this routine (except for the stomach curls and push-up burnouts) two workouts ago trying to avoid the plateau. I was taught how to use proper form when weightlifting but after this whole year and 2 months I feel I haven't gotten any physical changes. However, its obvious that I've gotten stronger, but like I said the muscle just isn't showing for some reason. Will someone please explain to me if I'm doing something wrong.