[Red Herring]

As Bibio says you need to just keep a regular eye on the traffic behind you using your mirrors and then check your blind spot either when a particular manoeuvre requires it or you have "lost" a vehicle you saw in your mirrors moments earlier and you now need to know where it has gone. Shoulder checks tend to be more important on multi lane roads where a vehicle can lurk in your mirror blind spot for a while so just try and work on your awareness in those situations and keep feeding the need to know what's around you. Once your confidence builds you will find this considerably easier than at the moment when it just feels like everything is coming at you from all directions!