I'm not a doctor but I have had experience with pain and swelling in my knee and trying to regain rom. I understand it feels like it's never going to end, like you're always going to be stuck in the position you're in and you can feel like you're "behind."
It sounds like since they went in the second time and cleaned things out, that you're having less pain and swelling, so that's progress. Keep in mind that 50 flexion is much better than 0, so that's something to hold on to. Let yourself have time to improve, don't force or impose timelines on yourself that may or may not be realistic.
I can tell you that I believe you will eventually get better, just stick to your pt's instructions and be patient with yourself. Your body is trying to do what it knows to do, but it has some obstacles to overcome so be patient with it and help it the best you can.