i've noticed recently that when i make love on top my legs become incredibly stiff and hurt so much after just 10 or 15 mins to the point that i can hardly move them. What do you think the reason for this could be and how can i rectify it? i'm 24 and do have low blood pressure and i have the contraceptive injection, i can't remember which one it is but the nurse said it does make your bones a little brittle, could these have anything to do with it?