Preg. symptoms but BFN

Okay, so i thought what i was experiencing were pregnancy sypmtoms (peeing more often, back pain, sudden headaches, yawning more often, nipples burning, and i just feel bloated)also my period was almost 3 wks late and only lasted 3 days. 2 days of light bleeding (light red) and the last day brown spotting. i went to my ob/gyn and did a blood test. the results; normal. i waited about a week and took a hpt. negative. my mom, stepdad and aunt all insisted i was preg so i took another hpt and again negative. is there anyone who got all negative results only to find out they were in fact pregnant? could i be pregnant? if not what else can it be?

i also get dull aches in my lower back to the left like right above my hip. i read this could be a kidney stone which worrys me greatly but im not getting any pain while i urinate.