if it's your first injection and you're a virgin to the needle it's going to hurt like hell until your body adapts
the second time is better and it just keeps improving.that is unless your gear has too high of an alcohol content to it then you're going to need to cut it/dilute it with cottonseed or grapeseed oil.the first quad injection I did was years and years ago,and I remember how badly it hurt.just remember it will get better bro.be sure to work out the muscle you inject in,that will help tremendously.best of luck to you