M 25 years and me n my bf had unprotected sex 4 a month I gt my periods on da 25th I hav 31 cycle we den had unprotected sex again a week after my periods after 3 days wen I go 2 da toilet wen I pee it burns n wen I wipe ders dark blood on it bt its been 3 days nw and it didn't happen agen what culd it be,nd wen sumthing my pants or so touches my stomach it hurts like ders a knob or something in my stomach I get lower pains on da left side pls help me