You can find some really nonsensical claims about low-carb diets online. They "wreck your thyroid" (untrue), or "bring on menopause" (also untrue), or "cause you to be more carb-sensitive" (true in the short term, till your system switches the enzymes it's making...).
Cuz ya know what DOES cause some of those things? GETTING OLDER. While you were living life and trying to get thinner and fitter, time kept a-marchin' on. This was a point that Jackie Eberstein (Dr Atkins' assistant) made on our first LC cruise, which impressed J and me so much. People used to complain to the doc that they had a hard time losing like they used to and often had to be reminded that -- hey, you're NOT twenty-five anymore! You're not even ... the age you were, five years ago (duh). Time makes a HUGE difference, especially to women.
Even though people in the fat-loss field are fond of discussing hormones in isolation, not only do a lot of them do more than one thing, they also do their jobs in combination with each other. And the estrogens are VERY fond of exerting their nasty sneaky ways on various glands -- thyroids, for a prime example.
Whereas estrogen acts to positively modulate the behaviors of insulin and cortisol in our youth, when it starts to diminish (beginning in one's THIRTIES), those two "weight-gain bullies" run amok ... and it grows worse as time progresses.
This is why the vast majority of middle-aged women in the west are overweight. EVERYTHING mainstream sources tell us to do is counterproductive: starve ourselves on restricted quantities of healthywholegrains, and get lots of exercise! RAISE them cortisol levels!!!
Middle-aged women are more carb-sensitive than they used to be. That's an endocrinological fact. We each have our own tolerance limits, depending on how our genetics predispose us and how much we've pushed our limits in the past. No matter how high or low it was before, it's less NOW.
We're more easily stressed, too, for the same reasons. Stress not only makes us less happy, it encourages visceral fat storage, which is never a good thing. No matter how easy-going (or not) you were in the past, under the same conditions you're MORE stressed NOW.
Do yourself a favor -- admit you have to live your life a little differently than you used to. You don't have to "take it easy" but you should probably take it easiER as time goes by. You don't have to go full-on low-carb (if you still tolerate them decently) ... but you should probably go lowER. Realize that you need to be a little more careful, because (at the same fitness level) you can now injure more easily. You possibly need more protein, as well as more vitamins and minerals (or more absorbable forms of them), because you don't absorb them as well as you used to.
None of us WANT to acknowledge that we're on a downhill slope, but when you're at my place in life, the fact is forced upon you. It's just the way it IS. "Aging well" is one of the main reasons I do the things I do -- watch my carbs, watch the Neolithic Agents of Disease, watch my stress levels.... I KNOW i'm not the physical specimen I was at twenty, or thirty, or even forty. But at sixty, I anticipate being a better specimen than I was, before I started all these amendments!