Tina - my first impression was gallstones although that pain is normally on the upper right side and can radiate to the back - often with nausea. Even gallstones can be life threatening if they obstruct the duct and cause a rupture. This left side pain with radiating pain to the neck and left shoulder sounds frightening. If I were you - even at your young age - I really would head to the ER. Honestly I would. I am not trying to scare you further but the symtoms you describe really do warrant an urgent visit to get medical care. If nothing else - can you get a urgent message to your gyno via his answering service??? Stress that it is URGENT and he will hopefully call you TONIGHT.