What Causes Abdominal Cramping Along With Heavy Vaginal Bleeding Post Intake Of Plan B?

Hello! I had unprotected sex on March 13th (he did not pull out) which was the last day of my period. I then took the plan b pill within 12 hours. I experienced a heavy bleed 6 days later, lasting for 4 days. Three weeks later, I m now experiencing a hard lower abdomen, heavy cramping, slight gas and slightly tender breasts (I also occasionally breastfeed). I m not sure if my period is due by tomorrow or by my last bleed, which would be the 18th. I ve taken multiple pregnancy tests, but I also know only the last one would ve been anywhere near accurate. My question is does this all sound like my period is coming or am I possibly pregnant? Thank you for your time!