this is a difficult one! Do you know the first day of your last period? Did you write it down on the calendar? If not, and you are not pregnant, then you should start tracking it for future reference.
If you do know the day it started, then you can more or less calculate when your next period is due. Cycles can range anywhere from 20-35 days, and even shorter or longer than that!!! It's so hard to tell if you don't know your cycle range. I wish I could help you out more, but I really need more info, like
1-when was the first day of your last period?
2-how long is your usual cycle? (1st day of period to day before next one starts)
You say you don't have this info, so it's just guesswork speculating when your period is due. Again, I'm urging you very strongly to keep track of it from now on.
Those pains you mentioned could be anything! From gastroentiritis to pre-menstrual cramps to pregnancy! I'm hoping you go to the doctor and do a test there, or talk to your mom about it.
If you aren't pregnant please get on birth control as soon as possible, as having a baby is a lifelong commitment you don't sound ready for. Think about it; are you ready to be someone's mom for the rest of your life? If the answer is no, then get the birth control, it's going to make life easier for you in the long run.
I'm wishing you the best of luck, and hoping you aren't pregnant!