I was vomiting pretty heavily. while i was vomiting, i felt a pop on my left side. i went to the er but had no rib damage. is it something else?

Most likely: You pulled a muscle while you were sick. So long as you are getting better, and given the plain x-rays, I would suggest taking it easy and try not to worry about it. If you pulled a muscle you will probably notice it over the next 48 hours, and it should heal without any specific treatment other than rest. If you have any new problems, or continue to be violently ill, go back to hospital.