Leg amputation is the last resort. Before that is a knee replacement and you are unlikely to get one if you are in your 30s. Its a significant operation.
ACL ligament reconstruction is pretty standard.
You ideally need an MRI scan to see what is happening inside.
My first prot of call woudl be a sports physio - but looks like you areseeing a Dr so maybe they will refer you to a specialist.
I also have problems with my hips compensating for my weak side - all my msucle have tighted on my good side.
If you do not have laxity(looseness) i nthe need then it may be cartilage damage.
Sharp pain is abd and need slooking at.