What is my purpose in life

I am still searching. What am I good at and when will it come to me? I have been waiting, trying new things, and hoping. But none of that seems to fill the deep void inside of me.
I have friends who are becoming doctors and engineers. But what the hell do I have going for me? I really want to help people, in whatever career I end up with. I don't know in what way.
I don't see a clear path and time is slipping away. I like to hear as much advice as I can get from others about this, but no responses seem to ice down my nerves.
I want to die knowing I did something great for people in this lifetime. I have low confidence in my capabilites. Could I really go for a difficult major? Am I as smart as the other? 
My heads spins and the pressure is intense. I pray to meet my fate soon.