HELP!! ma girl wont believe me at all!!?

i love ma fiance nd we been 2gether since i was 12 nd she was 13. we r now 18 nd 19 nd gettin married very soon. ive never cheated on her nd she hasnt cheated on me ever but she thinks i have cheated. these girls keep callin ma moms (where we r livin) sayin dat they r pregnant wit ma baby nd ma girl is really upset nd she thinks its true but it aint. i think theyre just doin dat cuz theyre mad im wit a white girl. how can i prove i never cheated on her?? we r gettin an apartment together on friday but shes havin 2nd thoughts bout dat nd gettin married??? wat do i do???!! she hit me real hard da first time 1 of da girls called nd left nd wouldnt talk 2 me a while nd now shes all suspicious nd even quit her job.......