9 weeks pregnant and NO SEXUAL APPETITE

I am 9 weeks pregnant and for the past 5 or 6 weeks I have had no desire to have sex with my husband. I dont even think about sex as an option and I cant figure out why. I've heard of women wanting sex more but rarely have I ever heard of a women not wanting to have sex while pregnant! and normally my husband doesn't really ask to have sex alot but it seems like hes gotten an increased appetite for sex and it really frustrates me when he's constantly asking to have sex, knowing that I don't want to! but I also feel bad because if I don't do it who else will?? but then it gets frustrating again because I want to explain to him what's going on but I barely even know whats going on and I just want to cry because I feel like I cant do something so simple for my own husband.. somebody please help me figure out what is wrong with me