It could still be gall bladder, which is actually on your right side, not your left. Pain from a diseased gall bladder can radiate to other spots, and the center of your upper abdomen could definitely be from your gall bladder. The pain I felt from my gall bladder was mostly in my back. The largest scar I have from when mine was removed is in the upper center of my stomach.
Really, have your doc follow through on gall bladder tests. Your gall bladder can get bad enough that it won't matter what you eat, you can still get attacks. It's a miserable way to live, and I did it for way too long.