I'm not wure why at 125 pounds you feel you need to gain weight, but you simply need to take in more calories than you burn up. The best way to improve your physique is to eat a high protein, low fat diet and start exercising. You want to gain muscle and not fat. Usually alternating weight lifting every other day with aerobic exercise is best. If you have become "hyper" recently and have lost weight without trying and/or having difficulty sleeping it is possible you have an over-active thyroid, or some other medical condition which needs to be evaluated by a pyhsican.