Caught a yeast infection after having sex does this mean i have a weak immune system worried i have underlying cancer or something horrible help!

Educate yourself: Any guy can catch a yeast infection down there from a girl or just being himself. It's got nothing to do with your immune system. It's common. You're almost a grown man. One of the finest gifts you can give yourself and the women in your life is to be a responsible, educated lover. Start using condoms and read a couple of good books. And welcome to the new joys and responsibilities of being a man.