What Causes Burning And Pain At The Knee Cap?

Hello,



I am 24 years old and since about 18 years old i have had discomfort on my right knee. It is more the side of my kneecap that sometimes burns and aches if i sit for long periods of time in same spot and sometimes after excersise - and i feel the need to release tension by moving knee and or rubbing area. I gradually put up a fair bit of weight between 18-22 and since loosing some weight the knee has got considerably better. However if i havnt done excersise for a while (i do go to the gym at least 2 times a week) it feels worse when i do run about - i played tennis last night and the ache went all way up my thigh.



I am not sure but i feel as though there is an indentation (but could be from slight swelling)?



Any ideas would be appreciated thank.