Yeah i did ALOT of those ovulation calculators too. I've always had a weird period cycle tho. Part of the reason I thought I'd never have kids was because I've had cysts on my ovaries since I first started getting my period when I was 17. It often resulted in me not having my period for months, but in the last 6 months I finally started having a monthly period. Except I have more of a 35 day cycle. I can't really remember what days I had sex with the ex, except that it wasn't very often. Only when I was drinking or when he really pushed it.
Thanks. Yeah this is a terrible spot to be in. The only consolation is that I have excellent taste in guys, so I know the baby and I will be ok no matter what happens. Both guys know the situation, and both really want to be the father. My ex-fiance even said he'd help me raise the baby just like it was his own. So I guess if we can't really prove it's the new guys I'll just get back with my fiance and raise the baby with him, due to recent events.
March 27 to April 4 is what the online conception calculator said about your fertile window, with a possible ovulation date of March 30 or 31, though that is calculated with regular 28-day menstrual cycles, and would assume you ovulate right in the middle of your cycle. (Many women have longer or shorter cycles, and a woman can ovulate early or late in her cycle.)
Did you have sex right up to the very last day when you left your fiance? A lot will hinge on how close together the last time you had sex with your fiance was, compared to the first time you had sex with the new guy. If one night you were with your fiance and had sex, and the next night it was with the new guy (or if there was overlap), there is no way you can tell until the baby is born and you have a DNA test. This is even true if you get an early ultrasound. Nothing diagnostic at this stage can pinpoint it that closely. At 10 weeks, the ultrasound would be within a week, but not a lot more explanatory.
I'm sorry you are in this spot.