I just got my period four days ago and every time i sneeze or cough my uterus twitches (there is 0 pain). my period has not been as heavy as it usual. what could this be from? could i be pregnant and it's actually just implantation bleeding?

Likely a period, but: Wait. A positive pregnancy test can tell a woman that prior spotting was actually implantation spotting. It is hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. A urine pregnancy test gives a reliable result about 3 weeks after sex (3 weeks after when conception might have been) or 1 week after starting a "weird" period.