why am i getting my period twice a month?!

This month I have had my period twice...in the beginning of the month before i got my first period my stomach was hurting like CRAZY and then when my period started i didnt have that much blood flow but it started to get heavier and heavier and then it stopped...i started to get spotting after that and it stopped and now i got my period again and it is pretty heavy..i do not know why this is happening..i don't exercise excessively and i havnt had sex in a long time. i don't know what's going on...someone please give me advice asap! (serious answers only) thank you.