Why do I never want to have sex??

I have an amazing partner, and even before I was pregnant we would only have sex like once a week at most. I live him, and want to spend time with him but for the most part I do not want to do anything. What is wrong with me? The past 3 days he has been asking me but it's the LAST thing I want to do. So now he's super frustrated and so am I. I just dont want to be touched and I dont want to touch him. Help me!