I'm so hurt and MAD at myself. I feel like a whore! Never thought I'd be in this situation

Well here goes my embarrassing story. So my cycles are 26 days apart and my last period was July 15th . I had sex with a guy the 26th and then my current boyfriend on the 1st of August! I'm trying to figure out who is the father of my child. This is so embarrassing and I know this situation is dumb apparently so don't bash me or beat me up for it! I found out I was pregnant yesterday with a cheapie from Walmart and then took a clear blue digital that said 1-2 weeks pregnant! I looked online at the conception calculators and it keep saying I conceived the 26th which makes the other guy my child's father ! I don't know what to do I'm so depressed and embarrassed because I thought I would NEVER be in this situation! Are those calculations accurate? How would I know for sure what day I conceived. My fertile window was the 26 through the 1st according to glow.