first time mother

I just want to confirm the duedate? Is it always based on the the first day of last menstrual period? I happen to have irregular period. My last cycle started last february 8, 2020 upto the 12th of the same month. It happened that i didnt have period on the 8th of march so i checked using pregnancy test kit and it appeared to be negative at the time. Later, on the 14th of march, i started feeling stomach cramps and my breast aches alot. i thought my period is on the way but then nothing. Then on the 20th i checked again and it was positive. Is my duedate still around the 14th of november 2020