If what you're doing is intended to relieve their pain or help them, don't worry so much about causing more pain. Sure, IVs don't feel good, but I don't lose any sleep when I start one on someone when I know I'm doing it to help them.
Yesterday we had a patient who fell and broke his ankle in to a 90* angle. Sure, he didn't like us manipulating it for the splint and all the other stuff we did, but he sure did enjoy the morphine and relief from pain by being in a more comfortable position.