What Causes Brown Discharge After Unprotected Sex?

hi my name is mabel, i am 28 and i dont have any medical history.On the 5th of may i had unprotected sex and i took pills to prevent pregnancy.my perios was to be due on the 21st of may,but from on the 18th of may i started experiencing some brown looking substance from my virgina for 3days and after blood started coming out for 5-6days, after that i started to feel pain at the left side of my tummy, constant headache and my tummy gets bigger at times. i still didnt stay away from unprotected sex, but i have not used any pill since then. is my womb ok and is it possible to be pregnant? thank u