Darn, that sounds really frustrating! Have you been sleeping plenty, waking up without an alarm? This is important for me personally to feel right… Perhaps there is a nutrient you are missing, an electrolyte. How do your legs feel exactly? Tight and achy, or sore or?
Perhaps you just need to walk half a mile, or whatever distance you can walk without a problem, do that a few days and see if you can be stable with that. Then rest a day and then try .75 miles, same thing and try working yourself up that way. Don’t forget rest days and certainly a rest week never hurt anyone. I always come back stronger after taking a whole week off from whatever I’ve been doing.