How can you tell if the rim is bent?

by Adriane
(Hawaii)

I know this may sound a little dumb, but here is my situation and question:
I have a Twinner that I love love love and it is used hardcore. We have thorns in our area that frequently puncture tires. It's a part of life and everyone deals with it. Usually I can remedy the punctures with fix-a-flat or slime, reinflate and go on until it's time to change the tube. Now I have one side of the stroller where the wheel will not stay inflated even to just go down the street. I have changed the tube multiple times. This is the side of the stroller that my oldest used to sit on and, I must admit, we exceeded the weight limit. He has also sat on the footrest of the stroller on that side while I pushed my other two for up to 1 mile daily coming to and/or from school. (So if you're keeping track that would be a 5yo, 2yo and 10month-er. Roughly 50+35+18=103lbs with 68lbs on one side) I am concerned that the rim is bent and rubbing thus causing the flats. It may just be time for a new stroller but convincing my husband is a challenge since he doesn't share my enthusiasm for jogging opposed to driving.

What are your thoughts and/ or suggestions?