Why wont my girlfriend let me put my hand down her pants?

i fully respect her doing what shes comfortable with but my girlfriend will give handjobs and oral sex all the time. and i feel like a douche when she does that and all i can do back is kiss her, she will let me rub her through the pants but that doesnt do anything 90% of the time i've tried to go under her pants but still outside her panties and she just pulls me away and says no i'll ask why and she cant give me straight answers just because i said so then i asked then when and she said 3 months for some reason i just want to return the favor but shes not comfortable with it shes already told me she was embarrasd about bumps she gets from shaving which i dont care about why wont she tell me the reason