It happens to everyone... you miss the gym for a week or more, and then you get ramped up to go back in.. then 10 mins on the treadmill your legs ITCH like crazy... so badly you want to stop.
Don't worry, you're not crazy, and you're not the only one.. (which I used to think)
What happens is when you adopt a more sedentary lifestyle for a week or more, your bodies doesn't need as many or as big of capillaries going to areas of your body (in this case your legs). So your body will shrink them.
But as your start exercising again, your body is Pushing blood and nutrients to your legs which causes those shrunken capillaries to expand = THE ITCH
Expanding Capillaries sound un-sexy.. but its actually a really great thing to have because your body will have more endurance.
Yes the Itching sucks.. and it makes you want to stop, but just keep pushing through it, It will go away after a few sessions showing You that your fitness level has moved from Sedentary = Active!
Now isn't that a good FB post?