Can anyone shed any light to whats going on with my youngster, snotty nose?!?

The white snot indicates it isnt a cold but a bacterial infection. He may have a low immune system ( he needs that tested) or you may need to look over the conditions you are keeping him and evaluate whether that is wha could make him sick. It isnt normal for horses to get sick so often. I would guess low imune system since he was in poor condition when you got him. Hope he gets better.