hello im 20 yrs old i finished my period on the 7 of agust then i had sex with my bf 4 days after my period we didnt use protection or anything ..the weird part was that i started to notice brown spots on my underwear and 2 weeks later i got my period on the 24.. my period comes every 28 days but this time it came way sooner..wat is the cause of this my friend said i could be pregnat but i got my period again.. i need an advice