it is okay for your breast to hurt even without a bra on

Breast pain is normal, bra or no bra. it has to do with hormonal changes in your cycle, or just growing pains.

well, there should be a reason for it. Nothing hurts for no reason

That's normal. I am the same way.

As all the others have said to some degree its perfectly normal but if it seems to start to do it more than it has or when you are not expecting it I would talk to someone so for now keep a note of dates when it does it and which side and see if there's any pattern to it. Then if you are further concerned go and talk to someone start by talking to your mum or at least a nurse.