Tendonitis is a condition of inflammation (just like any “itis”) and should not recur, or last more than about two weeks. If you have chronic pain, or recurring pain, then it is far more likely that you have tendonosis, which is an actual degeneration of the tendon. Left untreated, you may eventually need surgery.
The treatments for the two are very different. If you’re resting, icing, taking NSAIDs (the standard practice) and you have inflammation (i.e., tendonitis), then you will almost certainly get better. Conversely, if you’re doing this and don’t get better it’s a pretty good indicator that you don’t have tendonitis.
Doctors aren’t much help here, as most will diagnose any kind of tendon pain as “tendonitis”. But if the area isn’t red, or swollen, or hot to the touch, how can it be inflamed? Answer: it’s not, and your doctor is wrong. (Yes, this happens a lot with tendons.)
For more info on this subject, try looking at the Target Tendonitis blog. It has a lot of posts on various tendon pain problems, as well as a good ebook you can order if you want.