Hello Mandy and thanks for writing in
In my opinion it cannot be gall stones
because the pain is not constant. Yes it can be pulled muscles and you will get relief with analgesic
and anti-inflammatory drugs if it is it. In addition to this hot fermentation can help you.
I cannot rule out Plural Effusion because there is problem in lying down and breathing. To confirmation get you chest X-ray done if does not get relief from analgesic drugs. Plural effusion needs a medical attention.
Hope you get your answer.