period shorten to 2-3 days instead of 4-5days

hi, im 19 and sexually active. have sex once or twice every month with my bf-with protection. however, at the start we always did not use condom until 5-10 mins later. and then , last month my period only last about 2-3 days instead of 4-5days. And last month the colour of my period wasn't normal , DAY 1 - red but amt lesser than usual. DAY2-red but amt was less.DAY3-brown/black discharged. next day , pregnancy came out negative.Other than this , recently im always feeling bloated.