I know there are many different reasons for blisters on the stomach. But my suggestion to everyone would be to see a dermatologist immediately. It might be something minor that goes away on its own but it could also be a kind of blister that spreads or allergies.
I had blisters on my stomach, arms and legs for several weeks last July. I thought that I had a mite infestation at home and avoided going to the doctor. But when they didn't go away and spread even more, my sister dragged me to the hospital where I found out I had allergies.
The doctor said that if I hadn't received treatment in time, I could have had more serious complications. So you never know if stomach blisters are sign of a more significant problem and it's best to get it checked out as soon as possible.