Consistent moderate pain inner side of knee.while walking will "give out" with extreme stabbing pain in which I come very close to falling. No known injuries. Compared to other knee the knee cap looks to be double in size. Full extension even when sitting can Bring on the stabbing pain.
You're going to have to see an orthopedic surgeon and get some diagnostic pictures. Could be the meniscus. Could be a knee cap problem. Could be the patella tendon. Could be a cyst. But could bes don't help, you need to know so you can treat it.