I had exactly one shot of depo. I had no sex drive for the next 18 months, and gained about 40 lbs in the first 6 months. That stuff is bad news bears.
Right now I'm on the pill continuously (no placebo week, just keep taking the hormones all month) and I think it does affect my sex drive also, but not nearly as drastically.
I've heard of a medication they were developing to help women with low sex drives. If clearing the depo out of your system doesn't help, that could be something to look into. It could just be a chemical imbalance.
I've also found that I can get myself in the mood just by willing myself to get in the mood. It's really all in your head; there are enough lubes out there to circumvent the lack of physiological response. Sometimes I just need to "decide" to get in the mood, then I'll start fantasizing and thinking about sexy things, and that starts to get me actually in the mood.
And like Mag said, your partners could have their own role in it. People get complacent and stop making the effort. If you're feeling overworked, taken for granted, unappreciated, or uncared for, then your natural response is to become less interested in catering to his desires. Why should you if your own needs are not being met?
I don't need labels to define me. They're sticky and I hate the glue they leave behind.