BFN from a doctor's office But

Have any of you ever got a BFN (urine test) from your doctor but later got a BFP from a hpt? AF is due on02/28   or 03/01, I went to the doctor's office today to f/up on a UTI and they did a pregancy test and it came back negative I believe I'm 10-11 DPO. My boobs are really tender and sensitive to every little touch, I've also had headaches and a bit of a nausea. My PMS symptoms are usually different than this....thanks in advance for your feedback :-)