period dates: oct 15th, nov 14th, dec 11th, jan 1st

I had unprotected sex with my fiance December 29th and December 30th (I hadn't had sex anytime before that). We used the withdrawal method (which I'm aware fails sometimes). The unusual part of it all is that upon later research I found that my most fertile days occurred within that time frame. My period had started on December 11th of that month and ended around the 16th of that month. So, I believe that I was ovulating.

Except, my period came extremely early. On the first of January my period came on. So about 2-3 days after I had unprotected sex. The flow started off mild and tinged bright red, but in the last 2 days it was brown and scarce. The flow is not that abnormal for me, nor is the short span of how it only lasted 4 days, but the intense cramping I experienced was unusual. The cramping lasted for 3 days of the 4 and today I only had really minor cramping and lower back pain. I am still having lower back pain and really mild cramping, super gassy to the point of pain, and yesterday I was getting light headed/dizzy/nauseated out of no where. I think I should also add that I've been very fatigued and exhausted, which is normal on the first 2 days of my period, but usually doesn't extend any further than that. Other symptoms my breasts are more full but not painful, noticeable blue veins in breasts, random break out of bumps on face, hot flashes and very hot during sleep (I'm usually colder during my period).

My question is, is it possible that I still could have become pregnant since it was so close to my normal ovulating time frame, or was that all thrown off BEFORE I had sex and this early period is unrelated to me having unprotected sex? I know a lot of my symptoms could just be PMS but this is very irregular for me.. It just seems very strange to have a nearly 2 week early period right after I have sex. I would like to know if it is possible at all that I could be pregnant, or if it's not possible at all. Some suggestions would be much appreciated. Thanks