Cramps, plan b, headache?

Hi ladies,

It’s been 18 days since i’ve had unprotected sex and taken a plan b, which i had bled for 3-4 days 6 days after taking it (was just on my period a week before). Throughout these last 18 days since i’ve been nauseas on and off, had a headache, and cramping. Now for the last 2 days i’ve been having an almost constant pain in the middle of my lower uterus. Almost like a pinching or pulling feeling. What could all this mean? I had a negative pregnancy test today and my period should be starting in 6 days if the plan b didn’t delay it.