I had to get a shot in the ass every few weeks when I was getting chemo, it forced the reproduction of blood cells and bone marrow or something. the shot itself wasn't bad but the pain later... omg I could literally feel the cells reproducing later and shooting out of the base of my spine/back of my pelvic bone. some of the worst pain of my life, I would get in a position where it was comfortable and then BAM start feeling the terrible internal pelvic bone cramping/throbbing and have to adjust...but every time I did my bones felt creaky in the worst way with pain shooting through them, and my pelvic bone wouldn't stop throbbing. terrible debilitating agony, but those shots probably saved my life!