Can u actually hurt ur body by thinking something is wrong with u and then it happens because u constantly think about it? like make urself sick?

Power of intention: You're speaking to the power of "intention." the issue is a controversial one -- but certainly some would say that if you stress yourself out by worrying all the time, eventually you will break down your defenses (your immune system) & then you will indeed be more at risk for developing an illness. Perhaps think about speaking with a psychotherapist to help ease your hypochondriacal concerns?

Not usually: More likely people worry about getting sick then they coincidentally get sick. For example people worry about getting the flu, but then comes flu season and people get the flu.