Well, actually you should be very careful starting to practice again because the problem with the calcium breaking off will get really worse. My brother had the same Problem, with the same side of his collarbone and he had to quit football completely, because the doctor predicted that he might not be able to use his shoulder/arm properly in the future if he is not going to quit playing and practicing. If you get tackled wrong again, it might be, that you will have to quit forever. So just be a very careful and if you practice make sure the place of the clean break is always secured properly.