I had a normal period Dec 4th and it lasted 7 days I want to say, I had sex all throughout that month and on the 2nd of January he left out of town and I had sex with my ex.. I was sort of bleeding though that's the only reason I did it. I didn't think I could get pregnant while sort of bleeding still... It was on the 5th and 6th we did it. I was confirmed Jan 26 that I am 3 weeks pregnant according to my blood test. Who is the father please help!

Could be either one, impossible to tell without a DNA test.

There is no way to know who the father is until the baby is born and you have a DNA test.

You have 8/9 months to wait for the answer, but then what will you tell your boyfriend in the meantime, and how will you get them both to get tested to compare with your then born child's DNA?

Sorry but even at best trying to figure conception is only give or take a week.
There is no way to know at this point, as noted by the others, after the child is born a DNA test will have to be done to determine