While at the gym, I felt a sharp pain in my back and my abdomen started throbbing right away?

It depends. A little bit more information is needed here. Most likely this is muscle strain from overuse, but it could be a visceral problem like an ulcer or abdominal aortic aneurysm. If it only happened once i would write it off as over use, but if it keeps happening you should probably get it checked out with a medical professional.