Level a main and try that more actively. Twink brackets (especially 19) are very limited in what you can do. You can wsg, arena, make new gear sets, do useless crap (achievements, titles, tabards, etc), and maybe some world pvp just to mix it up. That really isn't much to do. Most likely you are switching class because you find yourself bored. Well if you have switched class this many times then honestly its probably not the class.. its probably the whole bracket.
So in my opinion start making a main and try each bracket as you level and maybe you'll find one with more variety to keep yourself interested. If not you'll end up at 80 and if you actually put the work into it there is no way you will lose interest in the 80 bracket so fast.
Personally at this point I only twink to be able to play wsg and AB competitively (and the community, but lately I've found it very immature). Other then that everything (arena, pve, class balance, etc) is better at 80, in my opinion.
Btw, I have made I think 8 twinks, but thats over 4 years of twinking. 2 of them were made because my only twink at the time was leveled. 2 were made because my guild moved into a new bracket. 1 was made because we wanted a druid FC over my pally. So I guess I don't really have your problem most of the twinks were made out of necessity (if that at all makes sense in a game).