Calculating Due Date!

Ch
Okay yall.....I'm hoping the dr can answer this but idk it that will be until Monday.... And the suspense is killing me! 
I have very irregular, sometimes lengthy periods with spotting spells. My last period started on Feb 6 and ended on Feb 23. Before then, I had some spotting spells sometime in Dec-Jan but I have no dates. I have no idea what my cycle length is bc it always varies. 
Glow says i had a high risk of pregnancy on Feb 27 and I had sex that day. On less fertile days (once again according to Glow), I also had sex. Those days where March 1, 7, 8, and 13. I experienced implantation bleeding on March 20, was able to see positive on HPT on March 22. 
Sooooo how do I calculate my due date?! I am not sure if I was ovulating on those less fertile days. I know they usually count from the day of your last period but mine are not normal so I don't think I'm that far along. 
Any help is greatly appreciated!! :)