What Could Cause Delay In Periods?

I'll try to cut this as short as I can...I have been off of birth control for about 4 months, my husband and I are not really TTC but if it happens, it happens. Ever since, I've tracked my periods and they've been consistently between 26 and 28 days since I've been off the Pill. Last month my period was due on April 21st, while we were on vacation. I didn't want to get my period while in paradise (who would?!) so I brought an unfinished pack of pills with me. I started cramping on April 20th and took 2 pills to try to stop my period for a few days. Ever since, I've had mild to average cramping, fatigue and sensitive nipples. My question is: Could two pills really mess up my cycle that bad to where my period 10+ days late? Or do you think it's more likely that I'm pregnant?