Having knee pain from kicking

Working with the heavy bag (150 lb bag) I have been working on my kicks. I started to notice while riding my recumbent bike, so knee pain. I took a few days off and one of those days decided to work on some kicks. I worked both sides doing 75-100 each side. I felt fine afterward, but that night I had almost cramps in my knees if that makes sense. I feel my technique is correct. I'm throwing my leg out slightly bent, trying to keep the leg loose. My instructor has said I need to turn my hips over more... THAT part I am having a hard time with. This is the first time I have had this issue though and perhaps it's possible that it's just to much kicking and my body just isn't used to it yet... but I don't think so.



I just cannot loosen up though. I have been tense since my first memories of fighting parents, constant stress, panic attacks, etc. so to just loosen up and fight sort of goes completely against what I am used to. Aside from taking a big dose of valium, how can I loosen up? Any ideas on the knee issues also?