No, it sounds to me like your glcogen reserves have been pretty much depleted.
The body can convert fat to energy only slowly. But the body holds glycogen reserves of about 2000 calories, which is normally more than enough to cope with the demands of exercise, and then replenish them later.
The brain is the biggest calorie burner in the body at about 600/day. Carbs are the preferred source of fuel for the brain, although in a pinch it can break down protein for what it needs. However, the brain cannot run on fat. And the body will sacrifice nearly everything else to keep the brain supplied with what it needs.
Carbs have about 4 calories per gram, so your 50g is about 200 calories worth. Your brain likely has been depleting your reserves to get what it needs. Combined with a fair bit of exercise, your glycogen reserves have run down to the point of empty, and bascially your body could only supply as much energy to your muscles as it could convert from fat (as noted above, this is a fairly slow process). Say a glycogen deficit of around 400 calories a day (add back what it has converted from protein, subtract glycogen burned during exercise) - I'm not surprised it has taken about a week to get to this point.
I'm not necessarily against low carbs (although I would single out simple carbs as being of greatest concern, rather than all carbs being the enemy), but 50 g is TOO low.
Quite apart from the low carb thing, I am guessing that you are burning around 500 calories a day with your cycling (very rough guess) - 1500 calories overall may not be enough to support this level of activity. Even at 1500, 40% carbs (which is the bottom end of most nutritionist's recommendations) would have you at 600 calories/150 grams.
PS. On re-reading, this all sounds like I am yelling at you - you have asked a genuine question, and don't deserve being yelled at. It's really intended to put a bit of math and a framework around what you need to eat to support yourself.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.
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