Irregular period, but is there another explanation other than pregnancy?

Patient: I’ve always had a really irregular period, sometimes up to 3 months in between, and I recently started taking the pill. Five days after I started it, I had unprotected sex, and about 10 days after I took a test because I figured it should be passed my “missed period”, but it came back negative. I haven’t had my period still and it’s been 14 days since the sex, and I’ve been having cramps for about a week that I usually only get the day before my period. Is there any other explanation or am I most likely pregnant, and when should I test again?