Well for me I was in a very similar situation, I didn't ride for maybe, 2-3 years or more. Going back in a had a lot of cramping.
I found the way to solve this was to buy fairly flexible boots, and not do with up too tight. It seems that if I tighten the liner up too much, I get the cramping. I would try keeping your boots very lose for a few runs, see if you still feel the cramping or not.
It could also be because you're using your feet too much to turn, instead of your weight. I am really in the same boat about the muscles but hey in a month it'll be all good!