Knee pain for 10 months

Wantefc

Im quite  heavy for a runner at 6 foot 4 though im reasonably slim.  im a hobby runner as opposed to a serious runner. though i have half marathons and plenty of 10ks under my belt.
Anyway since i hit 40 (im 46) i seem to be dogged with chronic injuries - i have had sciatica twice that mimic a hamstring strain. Since coming back from the last bout of sciatica last april i was gaining fitness back , i noticed my knees were a bit tender after runs but nothing alarming and it always settled down. I did  a park run mid april , nothing more taxing than usual and when i finished i noticed my left knee was more sore than usual. It has literally stayed the same since. Constant dull ache ( not painful) . I mostly feel it when im climbing stairs but its not every time i climb stairs. It seems to be right behind my kneecap. Even when i cant feel anything my knee just never feels right if that makes sense? I have seen numerous Private Physios who all prescribed various stretches that i do , all to no avail.
Finally i decided to go to the doctors who had my knee X-rayed ( nothing came back) and has referred me to the local Musculoskeletal clinic , i have an appointment next week.

The point of this post is to ask has anyone had anything similar??  its really hard to describe - like my knee is clunking inside.. The 1st physio i saw told me to stop spin class and running which i did. So i have had very little exercise in the last 10 months with no improvement. I want to start gentle jogging again but im scared it will make it worse and it seem counter intuative to go running with a sore knee.

my worry is Arthritis - if it is id sooner know but does that mean the end of my running?  Cycling has no interest for me whatsoever - i always feel like everyone is trying to kill me haha.