Why is my drive so low?

I'm 8 and half weeks preg and my drive has been non-existent over the past few weeks. I'm always so tired and after work I could go straight to bed(6pm). I feel horrible because we haven't has in almost three weeks. I feel like if I do it I will just be laying there waiting for him to finish so I can go to bed. The desire is not there and my sense of smell is so extra that I hate for him to try to kiss me now. Am I a horrible girlfriend? Should I be a trooper and lay there and let him get his or should he be supportive and wait until I'm feeling up to it? When will I feel up to it?