I have had this repetitive strain / motion syndrom too since 2012, but not at my fingertips, but in the tendons below the ellbow, first right, then partly left (after I changed to the left hand for using the computer mouse).
It occurs no matter how minimal the movements are, it has little to do with how hard a button has to be pressed, but just the thousands of repetitions are what causes the problem.

There are special stylus pens for capacitive touchscreens with a soft end, I would use one of those, I use it for my iPAD sometimes.