It could be that your not getting enough potassium? See your Dr and have him/her check your levels. If they're low then you might be prescribed potassium pills.
Did they use the arteries from your leg for the bi-pass surgery?
you should keep a journal of everything you eat/drink. what exercises you have done, change in meds...my husband gets cramps as well and we were able to pinpoint it to his cholest. meds and lack of h2o. Good luck! hope you figure it out!
I used to get leg cramps so bad my legs would move on their own from the spasms. Any time this would flare up I would take a product called Calm or Calm with Calcium. Calm is a magnesium powder and the other is the same, but with calcium. You mix it with boiling water and add your favorite juice, tea or drink it as is. My doc said it was most likely a calcium deficiency, but because the magnesium only one worked as well, it was obviously a magnesium deficiency. Either way, this product is taken by athletes for their sore muscles, too. Good luck! Just make sure you check with your doc. It's either Calcium or Magnesium that cannot be taken in high doses with blood pressure medications.