Did you have any early ultrasounds, such as in June, or July?
it could be either. you can still get pregnant with the pull out method. it isn't exactly effective.
April 2 on a Wednesday, HOW did you find out that you were 4 weeks? From the absence of your period? Or did you have an ultrasound?
If a guy has an erection within a few hours of having ejaculated and without having peed a few times, there is a possibility that sperm from the earlier ejaculation will still be alive in his urethra and will come out in the pre-ejaculatory fluid that seeps out from the erection. Despite not ejaculating, some errant sperm could come out of the urethra in the pre-ejaculate. (I am assuming you are saying all sex with either guy was unprotected.) It's almost certainly too late for Mr. NoCome to remember if he had masturbated before having sex with you around the 16th and the 22nd of March. (Are you saying one guy was on the 16th and the other was on the 22nd, or are you saying that between those dates you had sex with both guys?)
How did you find out that you were exactly 4 weeks pregnant on April 2? That is an unusually early time in pregnancy to be so exact, since most ultrasounds are not able to see anything besides a moderate thickening of the uterine lining at 4 weeks.