First have you thyroid checked, if it's functioning normal then guess what you should do next? NOTHING! For whatever reason your metabolism is high, that's just the way you're made. I wouldn't try to eat more or eat food to put on weight because your body isn't like that. As long as your energy levels are high, which I assume they are since you are physically active, just keep eating whatever it is you've been eating and don't eat anything weird.
My metabolism is high too, and i tried the high protein thing and it didn't work, years ago I tried weight gain powders and they didn't work, and they won't work on you either because of your metabolism. Be glad your like that because there are a LOT of people who wish they had your "problem"! A lot of people have slow metabolism and they gain weight just breathing, and all the diets in the world don't work to help them lose it, you're the opposite, and all the diets in the world won't make you gain.
If you want to gain weight there is one thing I can think of...stop being physically active which means don't do anything physical at all, walk into stores as slow as you can and park near to doors so you don't have to walk far, set in a recliner for years eating chips and cookies like crazy, and drinking non diet soda like crazy, then after about 3 years come back and tell us how much weight you gained!! LOL!!!
Don't take vitamins, they're pretty much dubious anyways, if you are eating correctly then you're getting all the vitamins your body can use and or needs.