ive had tennis elbow/RSI (same thing) in both elbows over the past 10 years..worst of which was in my trowel arm..
doctors will only usually give you cortezone injections twice,and then if there giving you the right advice,they will tell you that rest/massage/anti inflam/and heat and ice will in time ease the discomfort..
but unfortunately its not always that easy to rest from the job you do every day.
mine was so severe that i couldnt pick up a glass of water without using both hands,it was extremely painfull.it extended through to my fingers and i was forced to rest.luckily i tile aswell so i managed to alternate my trade earnings in an attempt to rest up..
a good physio or osteopath will be more than helpfull in teaching you how to take care of it and to give you treatment for a few months to kick start the healing process.the massage is painful though,believe me..its worth it.
its the skimming that increases the damage,and it will only get more painful.
i wore a sports strap that i ordered through my physio,its worn on the forearm and velcroed snug..it issolates the movement of the muscles and reduces stress on the tendon that attatches them to your elbow,it works,but its down to you to make a decesion to rest and maybe diversify for a while in order to elongate your trade life..
it does get easier,but its something that you have to deal with..
try using spot boards instead of scooping from a bucket,come down a size in your finishing trowel too..both simple things that you would dismiss but they do help..
join a health plan if you can,if your like me and countless others in our job,injuries and time off is always a hastle..it pays to look after yourself.
huck