Patellar Tendonitis. How bad is it? How to fix it?

I have been told by my doctor I have patellar tendonitis, and have had it near 12 months now.
The knee has not improved within the 12 months although I have tried some physio but that didnt seem to help much. I have also tried resting constantly for near 3 months and not really noticed any major difference/improvement.

I have noticed that just under the kneecap on the bad knee the tendon seems to be getting thinner and was panicking that this is going to fade away to nothing. I have quite high kneecaps and not very strong inner thigh muscles compared to my outside. I was hoping someone would be able to give me an idea what level of tendonitis they think I have (I need to see a specialist I know)...

The pain is sharp when going upstairs and more-so downstairs when my leg is bent about 60 degrees. I can quickly bend my leg past the pain and can walk around on flat ground without any problems. I have now developed a very slight limp to avoid bearing any unnecessary weight on the knee.

How bad is this tendonitis(I have nothing to judge against bar some nightmare stories on this forum!), is it possible to get this back to normal? How?

Thanks.