I had sex with a guy August 10,then got back with my boyfriend August 18,and the doctor says my due date is may 29,I don't know who the father would be.Hopefully someone can help!It would be great if its my boyfriends baby.

It's impossible to say who the father is. Any potential fathers will have to take a DNA test find out which one is.

The dates are too close together. Remember that due dates are a best guess, and can be off by two weeks either way. You'll have to have a DNA test done once the baby is born.

I had sex August 9 then I got my period on the 15th,I got back with my boyfriend on 19 .ive been so stressed out because I'm almost due and I want to be sure that there's more of a chance that the baby is my boyfriends.im due may 28.

Impossible to determine from such little information.
If there is a paternity issues then a DNA test is the ONLY infallible method.

Guess what? There is no way to be sure until the baby is born and you have a DNA test done to see who the father is.