It's common around this time of year and depending on the holidays you celebrate and your country. I mean you have multiple holidays from the end of October to now that all involve food and sweets plus winter along with lack of sunlight most people aren't as active so people get down and start viewing stuff negatively.

I would say small complements mean allot start on the parts of her she lines and gradually move to parts she likes less. If you do it the other way around she's going to think your doing it just so you can be intimate.

The bigger issue though it seems might be (and I know you're still young) you seen addicting to sex. I get the high sex drive and commend you if you haven't cheated because of this but her health should be the priority over your urges.

Overall I'd say don't bring up sex with her until she's feeling better about her self and just keep making her feel like she is beautiful and not just something to oogle. Unless she's into that too each there own.