Back pain, abdominal pain and light spotting, could I be pregnant?

I am 39 and have been off the pill for 8 months trying to conceive. My af was due 3-5-09 which is always been a normal 28 cycle like clockwork. Light spotting started 3-8-09 with back aches and sharp abdomen pains. Two home pregnancy test taken both negative. What am I experience. Could this be implantation bleeding after my missed period - What should I do at this point.