I use a medication that uses a self-administered automatic pen injector, and I find it's a lot more painful on my right side than my left, and it varies enormously from one time to the next. It also varies enormously on whether it bleeds---usually just a little speck, but a few weeks ago (on the right side) it bled like crazy. Not really much volume, but like a cut. It was the first time that happened after about 120 injections. (Plus, I have recently found I get faint at the sight of blood coming out, so I nearly fainted as a result... blah.)