Three days late for AF, swollen /tingly, very moody - all PMS symptoms but always have pregnancy?

symptoms so confusing!! We are TTC and I'm just getting BFN's all the time. Got a form for a blood test if I don't get a BFP in the next few days. My last two pregnancies I got a BFP before AF started so I'm just concerned really. My last pregnancy ended at 18 weeks. Is there any correlation between m/c and late BFP's??