Take a break from training until the pain has gone. See a doctor if it persists though - better to be safe than sorry!
Running is great for losing weight but at 135kgs, you're going to be putting a lot of stress on you joints by pounding the pavements. You mentioned that you had done some shorter runs on the treadmill without any issues so you might be better off using that for the time being. The treadmill puts a lot less stress on your body - I use them for my 'rest day' runs. Also consider using other CV-focused equipment such as cross trainers that don't put as much stress on your joints.
The right shoes are important too and it shouldn't be too much of a hassle to get your gait analysis done - most places are open at the weekends.
Hi - I've recently started getting pain at the back/outside of my left knee when running. I don't get the pain on every run but when I do - it usually appears on some of my longer runs - usually at the 5 - 8 mile point. The pain goes away the moment I stop running. There is no noticeable swelling and absolutely no problems/symptoms when not running.
I'm guessing it's an over-use injury as I was training quite intensely for a HM that I ran a couple of weeks ago. During that race I got the pain at about 10 miles but it had gone away by about the 12 mile point.
Since that race I've rested up until today. I've just got back from a very slow 5 mile run though, and unfortunately the same pain returned again. I was hoping that the 2 weeks rest might have sorted it out.
Any opinions as to what the problem/treatment might be would be gratefully received.