No Sex Drive at Twenty Four

Patient: I am 24 years old, I have been married for almost three years and I have and 18 month old child. I am having problems with my bedroom relationship. Ever since I had my child I have not really wanted sex. It’s gotten worse lately. I start to feel like I want to have sex but when my husband and I are just about to I lose all interest in it. It’s like my mind is saying that I want to but my body puts the cold hold on. What could be the reason for it?