Anastasia,
I'm sorry that you are struggling so much right now...I so know what you are going through, it seems I spend every month worried that I'm pregnant even if I'm not late yet. I do know that in my experience, the more upset and worried I get the later my period comes. Try to relax, use some cbt and try to keep a positive thought. Maybe if you get yourself a little more calm, it will help. Let us know how you are doing.