Your ex bf from the 5th and in the following days and weeks is far more likely to be the dad than the guy from the 3rd. Conception date for a due date of March 7 is June 14. That would be too late for sperm from June 3 to still be viable. You could easily get pregnant from regular unprotected sex around that time, even if pulling out. It doesn't do anything to protect from pregnancy. Also, the "weeks" count does not start when you presumably conceived, it begins two weeks earlier, when you had your period. So pay more attention to your due date. If you count back from your due date, it says conception was around June 14.
Get a DNA test, with both guys, when the baby is born just so you will never have to wonder, but if I were you I would just do one of those drugstore tests, unless you need it for child-support proof. (If you need it for legal proof, go to a lab approved by the family courts in your area of jurisdiction, and be certain to test with both men. It gives everyone peace of mind when one man's test says 'yes' and the other one's test comes up 'no.') Everyone deserves to have proof, especially your child.