I carry a 7d BG with a 300 2.8 + 2x TC on one side on a Blackrapid, and another 7D with a 70-200 2.8 IS on the other side in a lowepro toploader with another lens or two. Sometimes, I also have my backpack with several more lenses on. Exercise helps...
But to the OP's problem, just wear the inserts. Find good shoes and wear them. Likely, you have an underlying problem exacerbated by the walking on concrete, which still exists whether or not it is flaring up, and could cause you hip, knee, and back problems. The inserts will help correct your gait to help avoid these problems...