UPDATE! Nonjudgmental opinions and advice please!

So I am currently dating my boyfriend whom I am pregnant by. Although at times I have concerns regarding the possibility of my child being his. 
Basically, in Dec/2016 I had unprotected sex with Guy A (He used the pull out method). It was a few days after my period on Dec 21st.
Soon after, I meet Guy B we didn't have sex much as my period is irregular and I was focused on when it would arrive. It came later than usual on Jan 26 2017 so I believe. It was unusually late which had me worried and it was really short. It was about 4 1/2 days long and was heavy the first 2 days and light on the last few days. It was still very odd. It ended on the 30th of Jan. 
Me and Guy B had plenty of unprotected sex once my so called period ended up until mid February 2017. 
Usually every other day we had sex and each time unprotected. 
So by the 23rd of Feb I took a pregnancy test and I was pregnant. My due date is Nov 2nd. 
Based off that my child was conceived Feb 9th and I would have had a positive test by Feb 23rd which is exactly what happened. 
BTW; I did take a pregnancy test or 2 within early and mid Jan as my period was later than I expected. Each was negative and eventually on the 26th of Jan i had a short aunt flow I assume.
 I am currently 19 weeks and everything seems to be on track according to my Obgyn. Maybe I'm just overthinking this? Please give me your opinions! Please no rude comments. I know how this sounds! I just want to be absolutely sure that my child belongs to Guy B!!
Update: I went to my doctors appointment. I didn't mention much detail about my situation, but I did ask if they were sure my due date was correct and if I wasn't further ahead In my pregnancy than realized. I was told that based off my ultrasounds there was probably like a two day difference but everything seemed to be correctly at pace and my due wouldn't change. So that means that I most likely conceived early February and that Guy B is the father. What a relief. If Guy A were the father I would be a month a head and not behind. So yeah that's good news to me!