Study for school after work out

I have a problem focusing on study after exercise. While I am sitting at desk, my legs ache that interferes my focus. My legs are so restless that I need to have a break. I often walk around the room or lie down on bed a while. Then I lose time for study! I remember now this was the one of reasons I quit my exercise when I went back to school in spring. I am not morning person, so doing exercise in the morning is not my option. Does anybody have suggestion how to reduce the restlessness of my legs, especially after exercise?

How is your potassium?

I've never really paid attention on potassium, but I don't think I have it too less. I eat green leafy vegs, banana, and chocolate(!).
Maybe I should drink more water...? I'll see. If drinking more water solves my problem, I will update here. Thanks!