Confused, could I be pregnant?!

I'm really confused. I've always thought I couldn't get pregnant and haven't been using contraception with my partner for over two years. We went on holiday in May. I had three days ofor bad cramps, similar to period pains but not period pains. Didn't think anything of it, thought my jeans were too tight. I'm now nearly three weeks late for my period. I've taken two hpts, both negative but today I've felt really sick all day! I feel different too. I'm normally pretty regular so being this late and getting negatives and now nausea is confusing me. I'm 40 in 6 months and would be over the moon if it was a miraculous conception and not early menopause! Anyone else had multiple false negatives but ended up pregnant?