Why does libido disappear in the first place and what can you do about it?

I'd say don't get your hopes up about two reasons - that's way too simplistic. In reality, there's a much broader spectrum, and usually everything works in combination. Hormonal fluctuations definitely play a role (especially when it comes to age-related changes or cycle irregularities), but your mind is equally active here. Stress, accumulated fatigue, relationship problems, even plain old sleep deprivation - all of this can kill your desire way more effectively than any hormonal imbalance.

My friend went through something similar once - about two years ago she completely lost interest, and her first instinct was to run to a doctor to check her hormones. Turned out the cause was constant work stress plus unspoken grievances with her partner. When she finally talked it through with him and sorted out her work situation, her libido came back on its own. Her tests showed her hormones were completely normal.

So here's the simple advice: don't look for one magic cause. Start with the basics - are you getting enough sleep, how are things with your partner, how overloaded are you. If that's all more or less fine, then yeah, it makes sense to go to a gynecologist and check your hormone levels. Sometimes it also helps to just bring back into your life the things that used to turn you on - but that takes work, some self-reflection, and possibly a conversation with your partner.