Serious cramps and slight itch in the vagina. tender breasts too. what's the cause?

Different issues: Your cramping could be normal, depending on where you are at in your cycle. An itch in the vagina can mean an yeast infection, you can try an over the counter anti-fungal. Tender breasts are associated with the days leading up to the one's cycle/period. Also associated with pregnancy. Sounds like you're likely due for your period?

Cramps: Depending on where you are at in your cycle, it could be ovulatory pain causing the cramping or the start of your period. You could have a yeast infection causing the vaginal itching and the breast tenderness can be caused by various factors including possible pregnancy or the onset of your period.