ACL DAMAGE?

I had an accident three weeks ago. I fell off of a stone bench on a trip and heard a loud pop and fell. When I tried to get up I immediately fell back down. I flew back to the United States and had an MRI done that showed I have a torn ACL, a sprain MCL, and a possible meniscus tear. The doctor has me doing physical therapy. However, I'm condcered because after 3 weeks I still cannot walk. Everytime I try to walk my knee buckles andI fall to the ground. I don't know if I should keep doing the physical therapy or if I should get a second opinion. The injury more serious than the doctor is telling me.