Yeah I am what you might call "experienced" when it comes to the subject. I don't know how bad it hurts if you have a normal clean break because the two times I've broken collar bones they have been really fucked up (I've broken each one once).
I did this on March 10th-
and then I had to get surgery so it now looks like this-
From what I've heard from people who have had even minor fractures of their clavicle, it is always pretty painfull, and if it is a good enough break it is supposed to be one of the most painful things to break. If it is a complete break you know it because you can see it when you don't have a shirt on. Run your finger along it and you will probably know whats up, but if you are having pain in that area get it looked at. The shoulder is super super complcated and lots can go wrong.