What Do Heavy Periods With Back Pain And Nausea Indicate?

In April my period lasted for about 10 days and this month I am now 6 days late. My periods been very heavy on days 2-4 and I have almost always been 3 days early giving me a cycle of 25 days. I took two pregnancy tests and they were both negative. Earlier this month, during ovulation I had really bad headaches but I thought they were due to allergies. I feel very tired, have lower back pain and feel achy in my legs and hip. I have also felt cramps and my breasts have been tender. My left breast had sharp pains the other night. I am never one to overreact or be paranoid, but I have never been this late before. How concerned should I be? I m thinking that I may have a cyst? Can this wait until Tuesday (it s Memorial Day weekend).