I've slept with two men within 3 weeks, who's it more likely to be the father

So I've slept with two men within 3 weeks first man I slept with on the 12th Jan and second man on the 2nd Feb and 4th Feb. After sleeping with the first man I went to my GP and asked for the morning after pill and he refused to give it to me as I came on my period a couple of hours later he said it was impossible to fall pregnant. My period lasted 5 days but was very light. So anyway about a week after I slept with second man I then did a pregnancy test and it came back not pregnant, couple days later it said 1-2 weeks pregnant. However I have been told by Doctors's that these tests are not to be trusted and since have also found out that it is not impossible to fall pregnant on your period. I haven't always had regular periods but for the last 3 months they had been normal 28 days cycle and I had been coming on my period exactly when I should have been. I have recently been for an early ultra sound and they measured me at 6 weeks and 5 days which is exactly 11 days between each men. Who's is it more likely to be? I am going out of my mind not knowing!