When you first start AAS injections, it's going to be painful. Some gear, like prop, can make you feel like you were hit with a bat! And thats good, high quality prop. Believe it or not, cyp is one of the less painful injections and Geneza makes some great, low pain products. Still, you are going to get some, possibly intense pain, as your muscles get used to the injections.
do you want to rotate sites? YES! It is 100% necessary to rotate. Don't do an injection in the same site, more than one time a wk, even less if you are still feeling pain when its been a wk. Heres a good article on Naps' message board that will give you some more detailed info. http://juicedmuscle.com/showthread.php?49-A-Guide-to-Safe-Injection-Technique