I had light brown vaginal fluid today. we had unprotected sex yesterday, he did not cum. i finished my period last saturday. im on birth control pills?

Monitor: Brown fluid usually indicates old blood. If you had some blood left over form your recent period that would mix with vaginal secretions form recent intercourse. If the discharge continues consider seeing a doctor for STD testing.

Get STD check: Being on birth control has a 1% failure rate even is taken correctly. Always have protected sex with a condom. Brown vaginal fluid could be a sign of a sexually transmitted disease - seek a doctor care for testing and treatment

Unprotected sex: Congratulations on using oral contraceptives. Used as directed, they are an effective method of preventing unwanted pregnancy. I strongly recommend using condoms as a barrier method which adds protection against STDs/STI. Best to be safe than to treat an infection later.