Hi Velvetee, with regards to your problem, I have experienced this. It was when I was depressed and I was on anti-depressants. I wasn't into sex for six years. Then I came off, and now I can't get enough. Which isn't always a good thing.
Something you should ask yourself first of all is, though, 'is it that I don't want to have sex at all' or that 'I don't want to have sex with my current partner'. For example, does the idea of another person make you long for sex? If you ask yourself these sorts of questions, you can determine whether you're not interested in sex with your current partner, or simply the idea sex in general. If anything, this will help you to evaluate the nature of the relationship with your partner.
Think about that and get back to me!