After ACL knee surgery I have a problem kneeling down.?

I had my ACL repaired about 2 years ago. I am now taking cles towards my EMT degree and recently had to get CPR certified. Most of the cl was spent kneeling over the manikins practicing. I could only do this a few times before the pain was unbearable. Does anyone have any tips of strengthening my knees both internally along with the outside of the knee to help with the pain from kneeling. Thanks.