DNA test negative both times

Hi ladies, so I need advice and help on something I just ask that you don't judge me, because I have done that enough myself over the past months, so I just had my baby she was born July 14, by c section but was scheduled first for the 26th of July later I was changed to the 18th of July. But well, I had a boyfriend and we broke up and I slept with someone else.. I slept with my ex the first week of November and with  this other guy on Halloween October 31st and I found out I was pregnant November 23rd well the baby was finally born and I as much as I wanted my ex to be the father I knew I need to take a dna test, so we did with both guys .. And the DNA test came back negative for both guys.. I couldn't believe. It.. So I slept with someone else but back in the last week of September the 21st.. 25th.... And I keep doing the math and it just doesn't add up .. If I got pregnant in September I would've been due in June as per all the conception calculators online.. Can someone help me figure this out? I am so confused was my doctor off by a whole month? Please help.