Yes, it's a strange sound for most of the world! But of course, it's simple and second-nature to someone born in the USA. What I can tell you, is that if you are curling your tongue, you can get a pretty good R sound, but it's not the way that we do it! There's an easier way, with practice. This woman has some very good videos on American pronunciation, including the American R sound. It gets pretty technical to understand, but I think if you spend some time with this video (and her other videos), and you practice making this sound, then your tongue will not have to hurt! :) https://www.youtube.com/watch?v=Jq_yIbrD01c And two more: https://www.youtube.com/watch?v=bYWlQur5g5s https://www.youtube.com/watch?v=lFOgJ-QZ3lQ And maybe try this, too: https://www.youtube.com/watch?v=IFlAxjA4_nA Good luck!