Could Severe Pain Under Sternum Be Due To Gall Stones Or Acid Reflux?

I have a lot of pain under my sternum and it goes to my back. It is very sore to the touch. I m a little nausea too but no fever. It started at 9:20 and it hasn t gotten any better and it s after 4 pm. I am laying on my left side the pain is too much if I lay on my right side. I had an ultrasound done in September and the doctor said I have quite a few gallstones. However when I had the endoscopy done he said he was going to treat me for acid reflux.