TTC symptoms

We are TTC. My last day of ovulation was the January 15th. I was due to get my period January 31st and still on the 5th day...nothing. I have taken 3 pregnancy tests one was the Friday before my period (morning), the 1st day of my expected period (evening), and the 3rd day of my expected period (evening). All negative tests. I have been having really bad lower back pains, cramping, headaches, dehydration, and serious exhaustion. I have an appt to see the doctor for blood tests but could the time of day you take a pregnant test effect the testing?? It's so strange because I just don't feel myself and missed period but all negative tests!!!!!