Sex isn't good anymore...

Rebecca
Me and my SO have been together 10 months, when we started having sex he always made me orgasm but the past two weeks when we have sex I don't enjoy it at all... He gets really upset about it. I feel like it's my fault. I haven't lost feelings for him and I'm always really turned on, but once we start I just lose the feeling to want to do it anymore... What do I do?