Are the dates right?

My last period was oct.2-5. I usually have a seven day period but this month it was only 4 days. A normal cycle for me is usually 28days. I had sex on the 6th of oct., the day after I came off of my period. I found out that I was pregnant on the 5th of nov. I was already late for my period and I went to the ER due to these bad cramps I was having and a fainting spell I had weeks before my period was due. At the er they told me that I was 5-6 wks pregnant and my due date was july9th. My due date was still the same at my u/s. I told my doc that I had sex the day after I came off of my period and she said that sounds about right. With that being said I knew that it was my ex’s baby. but we was going threw some problems and I ended up sleeping with someone else on the 19th but this is after the cramping and fainting spell started and happened. This was the only time me and this someone else had sex. we didn’t start with a condom but we finished with one. But I guess somewhere in the back of my head is a small what if. I am not a hoe or anything this is just something that happened and has been on my mind sense I’m getting close to my due date July 9th. I would just really like some advice.No negative comments please because this is real depressing.