I had protected sex on april 15, 3 days later i had my period. on may 18 i experienced brown discharge bc forgot to take my pills could i be pregnant?

Low likelihood but: ...anything's possible, so if concerned please check a home pregnancy test for your reassurance.

Unlikely.: Assuming you're taking standard pills, the brown discharge is withdrawal bleeding from forgetting to take the pill as scheduled. While no form of protection is 100% guaranteed to prevent pregnancy, conceiving after protected sex and while on the pill would be very rare. Consider an inexpensive home pregnancy test, or see your doctor if you have other symptoms as well.

No: The brown discharge may in fact be the beginnings of a period or withdrawal bleeding from the forgotten pills. You can always run a pregnancy test to be certain.

No: If you had a normal period since the last time you had intercourse, you are not pregnant. If it was not a normal period, especially if it was lighter than normal, then you should check a pregnancy test to find out for sure.