Ok, I'm no Dr by all means, but tendonitis is an overuse injury and is cured by resting and even immobilizing the affected area.
Dude, if you can't bend your knee enough to get up a curb you need to take time off and heal that sucker up before you really do some damage. If left untreated you can cause permanent damage to your tendon(s), which can lead to permanent decrease of flexibility because of scar tissue build up.
I'm not trying to scare you, but I really don't think you should be running on it since you have such limited flexibility now. You'll probably need a good 2 weeks to feel much better and in 3 you'll probably be healed enough to begin starting a slow return to running program (4 would be better though).
I'm speaking from some experience since I've had tendonitis in my left knee and ran with, even finished my first HM wearing a huge side to side restrictive brace. Was it a good idea? No, but I knew that... I cut my runs way down hoping it would go away, but it didn't so I eliminated running for 2 full weeks then started back up very slowly for the first month. It nagged me a tad for a while after resuming running but nothing near like it was before resting it. It is now 99.5% healed now and I only really feel like I can strain that area if I stretch too aggressively. In hind sight, I should have taken 3 weeks off. I also had laterel epicondylytis aka "tennis elbow" which is tendonitis. I ignored it and it got really bad (I couldn't even hold an envelope between my fingers) I had to have surgery to clean up all the scar tissue in there. 6 weeks of movement therapy and 4 months of physical therapy and another 4 weeks of heavy duty therapy before I could return to work. On the positive side the elbow injury got me into running because I was getting fat.

Also on the positive the rest from running was really good for me apparently, because after building back up I was running faster than before.
It stinks to be injured and it stinks to take the time off, but it could stinks even worse if you don't.
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