still no af and negative tests!

Well Its now been nearly 3 weeks since af was due and a no show. I've tested twice every week with negitive results. I'm going to try go to the doctors tomorrow and try get a blood test but I don't think I'll get any results for a week? Not sure if that's true or not but it's what I've been told to expect. 
I've been reading a lot on google about people in the same boat as me and some folk have said they they eventually get a really bad period, could be stress or they get another negitive result from the bloods but then can still be pregnant. 
It really is a mind field of information out there. Nothing is really as simple as I had expected it would be!