I.G.
You should see an OB/GYN or a midwife. Pregnancy aside (which is an option) you could also have contracted an infection or STD.
If you are not intending to get pregnant also get educated about birth control.
If you do intend to have a baby, even more reason to get checked out, to make sure that you don't have a condition that may impact your fertility.
Anytime you experience unusual pain, unusual periods (over several months) or anything that makes you think something might not be right, you should really get it checked out.
Good luck!