Pain on back of knee and deficulty in squatting is knee (IDK) problem. You might be having meniscal injury, which can increase with improper physio.You need to consult ortho surgeon &confirm the diagnosis and get proper treatment.

Then find out these tests in google how to do. 1) posterior drawest test. 2) posterior sag sign. 3) slocum test for anterolateral - or anteromedial- rotatory instability. 4) varus sress test. U wil get the perfect diagnosis.. if u wil nt get the idea then consult with nearest physiotherapist. U need to do stretching exercises.. every 20 mint u should change ur posture style and legs position.. if is there sciatica then u should take stimulation therapy.. so i sugest u that once u should consult with ortho dr or physiotherapist.. I hope these wil help u.. Thanks.. TC