The second guy. The doctor would never have told you that you were only 8 weeks along if the father was the first guy. Did you have an ultrasound, or was the doctor just counting on a little cardboard wheel from your last period?
One thing your story prompts me to mention is that (in case you don't know), Plan B is intended to be taken only rarely, like once in two or three years. It's an "emergency" contraceptive for a reason -- it only works 7 times out of 8, and is also not good for you. Taking it every month would be a bad idea. After you have the baby, you're much better off getting onto a reliable form of b.c. like the Pill.
Anyway, the weeks count the doctor gave you suggests you got pregnant on or around December 24. That is so much later than when you had sex with Guy #1 that it seems puzzling that you are even wondering about the first guy. Has someone been saying something to you that makes you worry?