All of the above.

Keep the butt tucked in tight to your shoulder when shooting - that will help.

If it is a pretty light rifle the recoil will be worse - If so, I would invest in either a good recoil pad or one of the shoulder pads that you wear.

Hopefully it will get better with time - my first outing with a .308 left me pretty sore too. Now, I don' t even notice it after firing off 60 - 80rds out of my M1A in a session.