I'm not actually sure what you're asking.
I understand that your last three months of periods went like this:
Jan. 1: 4 days long
Jan. 25: (24-day cycle) 7 days long
Feb. 17: (24-day cycle) 7 days long
Mar. 21: (33-day cycle) late, 3 days long and very painful
Because of that, no, you would not be pregnant. A menstrual period is what your body does when the uterus is shedding its lining, which means no pregnancy occurred. It is not unusual to have an irregular cycle sometimes. I am guessing that your hormones just changed a little this month due to something (could even be stress), which caused you to be late.
Are you having unprotected sex? Are you trying to get pregnant? Why are you concerned that something is wrong with you?