Hi Rob

The pain mainly persists in the front of my knee cap, with after any form of exercise swelling appearing on the front of the knee cap and occasionally pain at the top of my shin bone.
It is a bit hard to tell what you have from your description. There are a number of structures close to that area that can be involved. Yes it could be inflammation of the patella tendon. Another possible structure is that there is a very intricate structure behind the patellar tendon call the fat pad and it is very sensitive to pain. this could have become irritated. there is also a bursa (a thin cushion of synovial tissue that lubricates between tendons and bone where they rub past each other) in the front of your knee cap that may have got inflamed. Another very common problem is patello-femoral pain due to "tracking" difficulties of the knee cap on the front of the knee. However that last options sounds a bit less likely.

Whenever I wake up my knee is really stiff, and I struggle to walk up or down any stairs without pain.
. The stiffness in the morning ((along with the swelling) is a sign of inflammation. Inflammation is worse first thing in the morning as the inflammatory process is more active at night and the tissue at rest swells - this eases off after a while as you starting moving the inflamed tissues around. Difficulty going down these stairs is common in any one of these problems listed above.

At this stage the proper diagnosis needs to be made and rest is really an inadequate treatment. One thing that really needs looking at is WHY the problem occurred in the first place and what keeps it being irritated. Often there are altered biomechanics that may put more than usual stresses on the structures in the front of the knee. This could be related to your childhood surgery and/or Imbalances in the muscles that control the knee could be part of the problem. Muscle imbalances are where one muscle is weak or lengthened out and one is strong and too shortened. A really good analysis of your walking and running is a good idea. Sometimes it isn't so much a biomechanical problem at the knee but due to the hip or ankle/foot so there are lots of things that can be looked at.

I suggest you go back to a competent sports or musculoskeletal physio who can do a good biomechanical analysis of what is going on as well as diagnose exactly what the offending tissue is. There are a lot of techniques that can be helpful once the problem is really well analysed.

In terms of managing the inflammatory component of the problem there are anti inflammatory gels that can help and sometimes the application of an ice pack can calm things down - these are of course immediate solutions - not getting to the crux of the problem - but they can help in the overall management.