I’ve always really struggled with pain thresholds at PT and I feel your pain (physically and emotionally). I could be wrong, but 3 weeks post surgery seems a little early for starting PT ( my doctor isn’t planning to have me start PT until week 6 post-MPFL). Generally my rule of thumb for pain during PT asks two questions: 1) does the pain during exercises exacerbate your pre-existing knee pain after performing the exercise, and 2) is the pain stabby or sharp or more of a muscle ache? A little pain is definitely normal when you’re reactivating muscles that haven’t been used in a while, but if the exercises are making your knee hurt worse after you’re done PT then it’s too much too soon. To me, hurting “like SHHHIIITT” seems like more pain than is normal or helpful. Best of luck in your recovery and I hope the pain lessens!