I was in a recent car accident, (rear ended by another driver while stopped at a red light, other driver going 30 mph), and I am noticing a bulge near my belly button that is roughly the size of a walnut. I think that I have a hernia and I am wondering if it could have been caused by my seat belt in the car accident?
Based on your description it seems possible that you are experiencing an “umbilical hernia”. Certainly a trauma to the belly can play a part in causing an umbilical hernia.
Here is a very thorough “Tutorial” from the NIH on Umbilical Hernia that might be helpful as you think this through.