Is it possilbe to prevent pregnancy with using only a condom? add diapharam?

Yes: No method is perfect, but using any 2 methods should be very effective at reducing your chances to get pregnant. It is more important to use the method correctly. With condoms, use only approved lubricants and pull out quickly after ejaculation. With the diaphragm, use it with approved spermicide and leave it in place for 8 hours after sex.