You'll have to have a DNA test done after birth, as Elyz said......however, if I had to GUESS, I would say it's your boyfriends if you ovulate mid-cycle.
Sorry to say this but you need to be honest with everyone and wait until you have the baby and get a DNA test done. Unless they are different races it'd be hard to tell just by looking at the baby. This is probably more common than you would think - a lot of people just don't want to talk about it. Did you have unprotected sex both times?
I told both potential fathers years ago when I got pregnant at age 20. One tested negative so I knew it was the other. I felt really trashy and terrible at the time but at least we all knew what was going on.