Is it normal to have a blister like thing with fluid in it 4 days after umbilical hernia surgery ??

Call or see your doc: Your may be irritated by the tape on your skin. If you were told to use an over the counter antibiotic ointment, that could also be causing the problem

Healing process: Sometimes fluid can accumulate under the skin as the body heals from surgery. If it's not very painful or red, then it's probably not an emergency, but the surgeon should be notified.