I know it's awkward, but you should see a doctor. Especially because you are feeling sick and have cramps. I got my period when I was 16, and I remember it just always being off, sometimes I'd get it more than once a month too. I ended up getting birth control to regulate it. Yours could just be out of whack this month, it happens. But with the cramps and feeling sick, it's definitely worth talking to a doc about it. They may want to do a pap test for that. Good luck!
I agree time to see a dr. You could have several different things wrong :/ If you wait it could make things worse. It could be fibroids or endometriosis or just an off period. But why take the chance. Best wishes.