I got my period on the right day but it only lasted 1-2 days and i've been on birth control for 4 months and he never cums inside me?

Check pregnancy test: The most likely cause of this is your new birth control. This often decreases the length of the cycle b/c no significant lining is forming in the uterus- so often there is only a small amount of blood. This is a benefit of the birth control. However since this is the first time you have seen this type of change in your cycle it would not hurt to check a pregnancy test.