Hi, i have a well grounded education in biology and chemistry, but it seems in the feild of tyhe womens response to hormones i am lacking. My girlfreind recieved the Depo Provera shot, a few days before she was expecting her period, she never got it, and it is now 3 weeks past, i can see how this may be normal, im not sure the exact role of progesterone. The reason i worry is one of pregnancy, allthough i cannot fashion it to be a possibility, anything is supposedly possibly. This may bring unimaginable stress into my life being i am only 17, and an aspiring doctor myself. I trust the medical opinion, is it probable the lack of period is from the shot??? It is her first shot, the only intercourse was beheld 3 days before the shot, and no semen was released, i understand the SLIGHT possibility of pregancy by precum, but this is a slight chance, this intercpourse was also late in the cycle, low fertility, im simply attempting to convince myself to discontinue my worries, thank you