Last sunday i had sex for the first time and the same day i started birth control pill. today i noticed a brown discharge, am i pregnant?

Maybe. Maybe not.: One can do a home urine pregnancy test if worried. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a withdrawal period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test.