The only guys I hang out with are my cousins. All non-family friends of mine are girls. So I suppose I can relate to your position in a minimal sort of way?
How can you feel more like a man? If you have long hair, cut it short in a ceasar cut. If you can grow some facial hair, then grow a shade. I prefer shaving myself, but who knows, it might help you. But definitely, definitely, definitely start lifting weights. Go buy a pair of dumbbells, and google a good mix of weight lifting techniques. It'll take months for the effects to show, but just dedicate 30 minutes every 2nd night to weight-lifting.
And probably the most important thing: get a girlfriend if you don't have one. The feeling of having a woman there to support you, and knowing you are available to support your woman, it really gave me a good feeling. Made me feel good, both as a man and as a person. No idea why.
And as LostMyMap says, look to any male role models in life. My uncle and my grandfather were the greatest men I ever knew. You need to be strong, bro.