little sexual activity in long term relationship.

Alexis
Anyone suffer from a low sex drive in your long term relationship? 
My boyfriend and I have been together for almost three years. We've been living together for about 6 months now. 
We both work full time. We're both in school. I start my full time school program In January so I'm certain that the sex we do have is only going to completely go away being we barely have any now. 
I've been told by my mom and doctor and friends that this is normal. That long term relationships suffer from this regularly. 
This only bothers me when I can tell it bothers him because I don't think about it the same as he does. I feel helpless and like a shitty girlfriend. What can I do to make this better?? I can't help it that I don't always feel like having sex like he does. I just need some advice. :(