Trouble getting worked up

I have been married for 7 years and my body does not respond to sex. I have to watch a movie read and book or even watch porn to get in the mood. I can have sex once in awhile and be just fine but my husband obviously needs it a lot and I can't work myself up so he has to go without. My best friend feels sorry for my husband because her and her SO have sex daily if not several times daily. What is wrong with me and how can I fix it? Is there any tips to get worked up without having to resort to other tactics? I think it hurts my husbands feelings when he can't work me up and I have to use other methods.