Severe Shoulder Pain?

so what started out as a dull pain has turned into a monster when i first noticed it hurting i just ignored it and it is steadily getting worse i can still move it just fine but handing a medium drink to someone feels like im handing them a ten pound weight the other day at work i was bringing ice to the counter which is about 30 feet away and the ice bucket is about 20lbs full and it felt like someone was trying to rip my shoulder out. It hurts to type, its hurts to to lay on it ..it hurts to do most things....a coach told me it probably isn't the rotator cuff ..what could it be?