Is my Girlfriend's low drive normal?

I'm not sure if it is the norm for guys to post on here but the advice I need should come from a woman's point of view anyway. I'm 22 and my girlfriend is 20, we have been together for 3 years and have never had the best of lifes but recently it has taken a dip for the worse. Most of the time when I try to initate she says she is too tired or has a headache and she would NEVER make the first move. On average I would say we have 1-2 times per week which I feel is way below average for a young couple. She says that we have a similar life to all the other girls she knows who are in a relationship but i dont know if I believe this. She also says that most women have no urge to have unless guys try to get them in the mood and even then it doesn't always work, again I find this hard to believe. Am I expecting too much from her to expect her to sleep with me more than this? I'm not a bad guy and love her too much to ever dream of cheating but I'm beginning to think this could cause big problems as we get older and it would benefit us both if I ended the relationship now?