What Causes Abdominal Pain And Post Coital Bleeding?

Hello .....I am a 21 yr old female and after having sex with my fianace today evening i saw my self bleeding when i used the washroom. The bleeding waz just like bleeding in periods but the concern iz that i have already had my periods a few days ago . Not to forget at one point while having sex i had pain and that pain troubled me for a long time and even now after soo many hours the pain iz still there at the left of my lower abdomen and back . I am very confused and scared as to what to do ,is it something to worry about as i am still bleeding is there any solutions or measures i can take without meeting a doctor . I did not have any sort of allergies or irritation before or even now so i guess it isnt of any STDs . Please answer and advice at the earliest .

Thank you