Hello, I Am 18 Years Old & I've Been On

Hello, I am 18 years old & I've been on the Birth Control, Depo Provera, for over a year & have never had any problems with it. I had to stop for a few months & started my period again & all was fine. I've been back on it for a few months now & it has been exactly like the first time. Bliss away from my period & cramps & all. But today I started bleeding after me & my fiance had intercourse, & a few hours later, the bleeding has gone back to the amount of my horrible periods, & my stomach won't stop cramping. I don't know if it is normal. Should I stop having sex until I know it's safe? -Lynn Patrick