Today, I had to click that little "my period is late" button. Again.

AF was due 5/6 and is now 13 days late, I'm about 18-20 dpo, and I've gotten 3 BFN on hpt(each test taken 4+ days after the last). My periods are irregular, though I've never skipped an entire month(besides when I got pregnant with my daughter, of course). I've had mild cramping on and off for the past 3-4 days. SO and I BDed a few nights ago, and the cramping became so excruciating that I couldn't move. The last two times we BDed though, no cramping at all. I do plan on seeing a doctor when I can. Any advice until then? TIA.