This is a perfect example of doctors not educating their patients! Tamoxifen only blocks the estrogen YOU ARE PRODUCING from the hormone receptors on a cancer cell. That is all. It DOES NOT prevent you from producing estrogen. And yes. You could get pregnant. (If you're having sex and haven't had sterilization).

and why do some people stop having periods? I was told it was very possible it would put me in menopause, however my periods just seem to be heavier and more frequent at this point :/

OK, don't mean to sound stupid, but if it only blocks the hormone recepters on the cancer cells alone, then why are hot flashes and other menopausal symptoms side effects of tamoxifen?

Tamoxifen doesn't stop your periods and only blocks estrogen. I had regular periods for a year while on Tamoxifen and now believe they've stopped because menopause has kicked in.