Is this wrong? I need help!

hi everyone. i need some help on this one. first off, i am 22 and an expecting father due in 4 months. i am unmarried and living with my girlfriend, whom i love very much. we get along fine and rarely fight. maybe a little bicker here and there. but for some reason i can't enjoy her pregnancy with her because i can't get the idea out of my head that it might not be my baby. even though she's given me no reason to think so, i'm still haunted by this constantly. my last relationship was brutally ripped apart in viewing a sonogram and discovering she concieved the child while i was away in military. i know this would have some affect but i wouldn't think this much. her background of cheating on every boyfriend she's ever had isn't comforting either, but seems like she's matured from that and is happy with me. what can i do to get this out of my head, or at least supress the thought? how would i tell my girlfriend that i want a paternity test to ease my mind?...or should she not know? i've already prayed about it and it's only become worse and bothering me more and more each day. someone give me something to go on here.

If you are still in the military and unmarried, once the baby is born you will be required to pay child support. Before the military can force you to do the paperwork, they will provide you the opportunity to do a paternity test. Just tell her it's mandatory.