Paternity test and don't know who's the father of my son?

Well to be short story . I had a sex with a guy 2times but I ended.we just were together in sep and oct of 2010.then in nov I went back with my real fianc� or to be honest I cheat on him, but then on nov 15 I had my period normal. Then after that I didn't get my period until dec 30 took a preg test and it came positive now iam 6 mnths pregnant but Iam unsure who's the daddy iam very confused cause if it were my ex boyfriend than I will be more than 6 months but i only have 6 months and will give birth on sep 16 ,,,,help someone who has been through this I mean Ian not perfect person