[Closed] Niggly knee pain - anyone had similar?

Have a bit of weird pain from the centre back of my left knee. It only hurts when I stand to pedal or pedal hard, for the rest of the time there is no pain whatsoever.

It sort of feels like the onset of cramp and feels like it will get worse if I try to push through it.

Can't seem to stretch the area either, hamstring / calf stretches seem to have no effect which is odd as I thought I might notice if it was something to do with them

Been like this for 18 months or so, definitely not serious enough to bother a doctor. Think I'll try to get a physio to take a look but wondering if anyone had similar and what you did about it?