Relationship Lonelinnes

Bros ı have gf we are happy in most situations but when it comes to sex she seems like she is not interested at all.When ı tell her about it she always has some excuses like hair or she says she is affraid of getting pregnant.This situation really makes me go crazy cause i think like she doesnt want me and she doesnt attracted to me.How can i fix this or what shoul i do in this situation.Im really depressed about it.