@anamur-- I'm sure a wax paraffin bath will help relieve your tendonitis symptoms. My wife has arthritis and she has found some relief with bi-weekly wax baths. I think the warmth of the wax helps with inflammation and pain.
There aren't any negative side effects of wax baths, so I think you can get it as often as you like. But it would be too expensive if you were to get it at a spa each time.
You should get a wax bath unit for the home like my wife did. It's available online. It's a basin and you melt the wax inside and dip your feet and hands in it. My wife keeps hers on all the time because it takes a while for the wax to melt after it has become solid.
I used it once too, it was nice.