Over 3 weeks late and negative tests

I'm so confused. I haven't gotten my period for now almost a month (will be April 8) and I have all negative test results. I started testing when I was one day late and then took 3 others every week I've been late. My body has been feeling weird but I just don't get it. I haven't called my midwife yet because last time I was 2 weeks late the nurse told me to wait a few more days. Figured I'd call Monday if I don't get AF this weekend. 
Hubby and I have been actively trying for 6months now. I track BBT cervix mucus and I use OPK
I know there's a chance the acid isn't strong enough to show up on urine tests and I could still be pregnant but I know in th back of my mind I know I'm probably not pregnant, again. Haven't been stressing and been trying to relax but just really want to get pregnant! Starting to get annoyed and impatient. Just wish I'd get either a BFP or AF so we can try again. 
Any advice? thanks :)