quad tendon pain

hi everyone
i am trying to find the best course of action for quad tendon pain and swelling.
i have had 4 op's to my right knee over the years 2 meniscus trims , 1 acl recon and 2 weeks ago a diagnostic scope of my right knee which came back with no further damage inside my knee. since april 09 i have had pain in my quad tendon in the vmo area and also just above the knee when trying to exercise the quads. i have very weak quads and even if i do 2x10 quad contractions and 2x10 slr it is painfull just after ex and the next day this flairs up. the muscle itself aches a little but the tendon pain is quite bad and it is hampering my ability to do the exercises.
i even use a cryocuff for 30 mins post ex but the pain still occurs. i also have a kneecap tracking issue now as my lateral quads have now become the only muscles that really work. i have read about cortisone injections and prolotherapy but i do not know if these are the options for me.

p.s i tried exercising through the pain about 3 months ago and i could not put weight on my leg for 4 days.
can anyone give me a nudge in the right direction?
at the moment i am doing 2 x 10 static quad contractions, 2 x 10 slr , 2 x 10 vmo squeeze then using cryocuff 20- 30 mins then rest for a day
hope someone can advise me