Lack of in our relationship ... what should I do?

Sorry kind of long here ..... Im not sure where to start with this because there is alot going on here ... its not so simple. But here it goes. Lately I feel like there has been a lack of in my relationship with my girlfriend. My drive is still the same as when I met her. But hers is not. When we first started going out we had like every day .. several times a day. There were even times when we talked about it and I told her that I need it every day .. you know its something that balances me out .. it keeps me sane I guess .. Im sorry but thats the way I am and most guys are probably this way too. And she was fine with that. At the time her drive matched mine. So it was awesome. Coming from a previous relationship where I only had it like maybe 2-3 times a month ... this was amazing. And she was kind, caring, compionate too. I thought I had everything I wanted. But lately things have gone downhill. You know .. she has a new job as a nanny for this 7 month old baby ... this kid cries all the freaking time. So I guess maybe it wears her out. But she used to have a similar job farther away and the was still great back then. And she cooks for me when she comes home which I really do appreciate. But you know .. Im in the military and I work 8+ hours a day (sometimes 10-12), work out for 2 hours, and then come home and do some chores like laundry, dishes, etc. Im not a couch potato. So we both work equally (I guess you can say this). I got really upset one day when she came home and started giving me all these signals that we were going to have sex tonight ... grabbing me ... touching me ... teasing me ... telling me Im hers tonight ... and then I get the clic "Im tired" when we are both in bed. When I heard that I felt so disappointed and upset ... but I had to be a trooper and put on my supportive face ... but that night my mind festered ... I was so angry and didnt sleep well ... and I didnt like feeling that way but I couldnt help it ... and the next morning I sure did show in my demeanor ... at that point I really couldnt help it ... Im not violent or aggressive ... but I gave her the cold shoulder when she came to say goodbye to me to go to work ... she knew something was wrong and I told her what was going on later that day ... so we got into an argument ... that night when she came home I talked to her ... you know we have talked about this before ... and there are too many excuses to know which one is the right one ... she tells me im too big and it hurts ... she tells me she is tired ... she tells me I need to do more for her ... and some of the other things she told me made me feel even worse ... we started talking about our past relationships and she mentioned to me that she had sex with her ex boyfriend every day ... her ex boyfriend was a POS ... he treated her so badly .. called her stupid, retard, other bad names ... lied to her about what he did for a living ... abused her verbally, and stole money from her ... and yet even after all this she still let him have his way with her every day. Im not like this at all ... Im a pretty damn good boyfriend if I do say so myself ... but it hurt me to know that this ****** got what he wanted ... so then I told her that this pretty much confirms my theory ... guys who treat women like trash get what they want from them ... I would never resort to this type of life but its sad ... I already know of 4 or 5 other relationships in which men treat women this way and they get what they want ... when I said this she was silent .. and then we both went to bed ... problem unresolved ... and the next day I thought .. you know I really miss her and I have the day off so Im going to go surprise her at work ... and so I did ... and she really appreciated it ... but that night I wanted her so badly ... and she tells me she is tired .... and I have to be supportive right? ... deep inside I was so upset ... but I didnt show it ... I hate keeping these feelings inside .. or even having them at all ... Im not sure what to do anymore ... we have had so many talks about this in which she agrees with me and then changes her mind but tries to interpret what she said before another way ... I think Im doing the right thing here by talking about it but, man, its so frustrating ... I dont know what to do.................................