It sounds as though your condition is something like my own. Although I haven't been diagnosed as having costochondritis doctors have previously checked me for it because of the combination of respiratory failure and the painful difficulty I have raising my arms, and inability to press my arms, in front of my body. It's likely that you will find it relatively easy lifting your arms to the sides or performing pressing motions to the side. That's the reduction in chest muscle function resulting from sternum/muscle cartilage function. Mine resulted in bursitis in my shoulders as well. In my own case I believe that overexertion was the cause, consistent with both having occurred as a consequence of the same cause.

As for the issues with increased allergic response it's likely similar to how my own respiratory failure has affected any of my own conditions which also affect my breathing, making them more serious because the pectoral muscles don't respond to support increased breathing. Out of interest, has your own loss of function affected your abdominal muscles like my own? I haven't been able to engage my abdominal muscles, in order to sit up, since my condition commenced.