So after a few weeks of physiotherapy and now that we can see all the swelling has gone down... I've definitely partially torn my PCL. None of the physiotherapists understand how it could have happened, so it might actually be an old injury that just got aggravated by other activities I was doing which caused the swelling.
Going to see a doctor next week to schedule an MRI to take a good look at what exactly is happening with my leg. Hopefully I can get back to doing legs again soon - don't want to look like I just work beach muscles at the gym.