I know this is a tough thing to ask of someone active (and it was very difficult for me to do). Can you stop ALL activity other than necessary walking for 3-4 weeks? Then start back slowly and gradually. If it's tendonitis, it may be enough of a break to reset things. If it calms down during the rest but restarts as soon as you start back up, that will give them more info. That's what I ended up doing at about 6 or 7 months. My PT was concerned at how even manual stretching by him caused pain during the rest phase so we didn't even do that - just lots of massaging. The pain was decreased during the rest phase but started back up full force when I did anything after.
All of the info you can accumulate about what hurts and what doesn't and what helps and what doesn't provides valuable info to finding a solution. The Eureka moment for a scientist usually isn't the first attempt but the attempt that comes from the knowledge gained from the "failures."
Keep your head up and keep looking for the solution. It may not seem like it sometimes, but you're moving forwards towards the solution.