10 days late Neg test x3 HELP!

My husband and I have been TTC for six months now. I was on the pill for 12 years previous to this and my periods have been all over the place. PT says I'm 8 days late now and I've taken 3 tests that have all come back BFNs. I was experiencing some weird tingling in my uterus for about 3 weeks and had some major back pain when I thought implantation would occur. I also had two days cramping when AF was due but nothing since then. Anyone have any ideas what could be going on?