What Causes Abnormal Vaginal Bleeding?

Hi doc I m just a bit worried I had a normal period on the 30th of August and it finished on 6 September I then had unprotected sex with my partner on the 8th and 10th of September. I then began to bleed again on the 14th of September which has lasted five days but still has not stopped Im a bit confused on what s going on ? can you give me your advice on what I should do or what s happening to me