120 Cadence?
You may do fast pedal intervals at 120, I don't think it would be too comfy to do 120 rpm regularly unless you have a naturally high cadence. (which I don't) Cadence of 90 - 100 is plenty high for most of us.
Make sure your saddle is high enough. Make sure your seat post is clamped tight so it doesn't slide back down as you ride. A little fine sand on the post works well for slippery posts. Especially when 245 pounds of @$$ is on that puppy for hours at a time.
When going up a hill make sure you keep your cadence at least at 70-80 if not higher. Shift into lower gears, get a triple if you don't already.
If pain persists see a specialist and take some time off the bike. Stretch (I don't much, but i guess you're supposed to.) Tendonitis is serious and can ruin the fun of cycling. When I get a flare up I take it easy, especially on hills and use glucosamine sulfate (much cheaper than Glucosamine and Chondroitin) and flax oil.
Gregg