I think that's a pretty normal response to a bigger workload than you're used to. I don't really work out my legs as much as I honestly should, I basically never run, and I am not as disciplined with my sprints. Yesterday however I went to muaythai and decided to go for a run that's about 1.5 miles. No issues during the run, no issues during the workout, we finished with 50 deep bodyweight squats with calf raises at the end (squat down, as you stand up finish with a calf raise) and today my legs are sore as shit, and I'm pretty certain tomorrow will be worse than today.
The worst I ever experienced was during The Spartan Race. The whole race was beyond brutal, but there was a part where they had this ridiculous long incline, it was muddy and there was barb-wire so you were supposed to get on your hands and knees to go through it. Took me like a half hour, then as soon as I got to my feet... PAIN. My quads felt like rubber bands. I was literally scared to move because I felt like every time I took a step they would pull. I was cramping as I walked, the pain was pretty serious. It faded eventually. Something about that rest period though, where I basically didn't use my quads that much, made them cramp up when I needed them again.
On another occasion, I worked out with Al Kavadlo and others, and did much more than I'm used to as far as pull ups, dips, etc are concerned. The next three days I didn't do shit but rest because my muscles just ached.
My guess is that hike was many more "single leg squats" than you're used to. I don't really think much more than that is happening.
Question, can we see the backside? no just kidding, how come you're trying to low-carb? How low-carb are you talking? it may do you good to have some carbs maybe post-workout on your heaviest day. Not too much, I'm not talking about re-feeds or anything like that, but for me if I go low-carb too long I retain water more and there's a bit of a "swoosh" effect when I do have carbs. Also, are you squating daily? how come?