No sex drive

Lately I have had absolutely no sex drive. Me and my boyfriend usually have sex about three times a week, but now it's been 3 weeks. He wants it but I just don't feel like it, not even during my ovulation time. I also don't get it because we have been trying new things and it has been pretty amazing, but still I don't want to have sex. Have any of you been through this and how do I fix it?