I had the same issue with my arms getting tired. But I discovered that once you have the different tapping points memorized, you don't actually need to use your arms. You can just imagine yourself tapping on the points and it works just as well.
The setup statement is actually the most important thing to get good results.
Anyway, it works well for me for anxiety and it depends on the type of pain. I get multi day headaches from barometer changes. The EFT works for a few minutes, then the headache comes back, and I have to keep repeating it. Healing touch therapy works better for me for this long term kind of pain.
On the other hand, I did have a "one minute wonder" one time. I barked my shin tripping up the stairs. I had a big swelled area that hurt like heck and I figured I would have a big bruise from it. I did some EFT, and the pain went away. I forgot about my shin, but when I looked down about 20 minutes later, the swelling was gone, and I never did get a bruise from it!