Ive been 2 months with pain in my leg, today i was walking backwards and i berely touched the back of my knee with the sofa and my knee failed and hurted so much like i hit it strongly. now my legs is not just bothering but in pain, what can this be?

You need to elaborate more on the symptoms. Pain location (knee, ankle, foot of one or both legs), any swelling in the posterior aspect of your knee after you hit the sofa, what movement makes the pain worse (standing, walking, go up stair, bending the knee, etc.). Because this is a chronic pain, exacerbated with a minor injury, it's still better to see a doctor for a thorough exam and tests.

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a doctor. Wish you good health!