There are only two possible reasons why you're not achieving any fitness goal.
1) Your nutrition is lacking.
2) Your training is lacking.
In that order. If you're going to the gym and hitting the weights hard, then it's probably your nutrition that's weak. As a beginner to weight training there are several reasons you may not be seeing a weight gain. As a beginner any weight training routine will work, as long as you're working hard.
The first, and most likely, if you truly are eating over your maintenance calories, is that you're losing fat and building muscle at the same time. While this is normally impossible to do--lose significant amounts of fat while gaining significant amounts of muscle--as a beginner almost anything will work freakishly well.
The second is that if the level of weight training you're undertaking is completely new to your body, your body first spends 3-6 weeks or so optimizing what it has before actually building any new muscle. It does this because it's a very clever biological machine that is programmed to be as efficient as possible.
The third is that you're not eating enough calories, because you're a lazy knob and haven't figured out what your BMR is and how much more than your BMR to eat. Quit being a knob. It takes like 5 minutes. Google is your friend. I can tell you what your BMR is off the top of my head, for someone who's moderately active, 16 yrs old and 157 lbs, assuming about 12% bf, your maintenance caloric intake is ~ 2700 and to gain weight you should eat ~ 3200. (~ = approximately, + or - 25 calories)
One more thing..find some way to measure your bodyfat every time you weigh yourself. You can get skinfold calipers for $10 that are accurate enough. You don't know **** unless you measure your bodyfat as well as your weight to determine whether you gained/lost fat and gained/lost muscle.
After you're out of the 2 month period, if you feel like something's not working..adjust one variable at a time (calories in, training routine, whatever) and give it at least two weeks to observe the results. Always try to use scientific method rather than whim.
