hate having sex with husband

I hate having sex with my husband. 
I don't know what to do. 
He's generally a really good man 
He's loyal hard working etc. 
I just can't stand having sex with him. 
Everytime he puts his mouth on me or touches my body I just feel disgusted and tense up. It didn't use to be like this we had an insane sex life. I don't know what to do. We have a 15 month old and I don't want to break up our family but I'm only 23 and I'm not sure I can live the rest of my life like this. I pretty much just turn of my mind and do what I have to do to get through the moment. We've been together 4 years and married for 2. Please no nasty comments I haven't done anything wrong like cheat this is all just a thought process I've been keeping to myself for the past year. I need advice. 
And no I'm not depressed ....