Why is sex before marriage, using a condom, and master bating a sin in God's eye?

I mean are you serious? I only want three kids and i don't think there is any way in hell i could just not have sex for the rest of my life, it is even a proven fact that sex is important to a healthy relationship but then god will be mad at me. I mean does he want 40+ kids to die or starve or be put up for adoption and not know their parents because i cannot take care of all those damn kids. What the hell do i do?