Some bags leave space for you to run the camera strap outside the case so you can carry it over your shouldler or neck but still inside the bag protected.
Have a look in the camera shop you bought it for size, also have a look
here for a rough idea of size/type and most bag manufacturers have pretty good websites of their own once you have a rough idea showing the interior and example shots.
I went from having an over the shoulder Crumpler Pretty Boy to a Thinktank rucksack as I didn't like it on my shoulder and preferred to have both hands free etc, I ride a motorbike and a mountain bike which I both use rucksacks on so am kind of used to having something on my back.