I've been experiencing either lower abdomen or pelvic cramps, breast tenderness, frequent urination, and frequent headaches. what's going on?

Depends: If you're sexually active ; have had relations over past several weeks with a fertile man then, your symptoms could point to a pregnancy. If you are not sexually active or if you are but have been abstinent for the past several weeks to month then, you may have a urinary tract infection though breast tenderness really isn't explained well by that diagnosis. Visit to your doctor would be good.