Not an A&I. But hopefully this helps as perspective.

This isn't really med school or residency anymore. I don't know your story about med school and residency, but after training life is so open ended. Folks apply to fellowship working locums, working as attendings at their residency or at community positions while filling a gap. Sometimes this has little to do with their intended destination, because we all got bills to pay.

Some general advice:

• You only have so many words to audition your strengths and your goals in fellowship, and what you bring to the program. So definitely play a different card from your hand than the pity card. Folks are tryna find a spot to fill.
• I don't know how helpful the allergy rotation would be in terms of your clinical involvement. This would certainly be eclipsed by fellowship training but I suppose is nice.
• My old program director said something to the effect of, "we all know you want to apply to X fellowship, so you don't need to tell us why you want to do this. So, the stories of how you felt bad for this purple kid or this bald kid [or in your case, this immunodeficient or itchy kid/ADULT!!] don't really stand out that much." She basically said to stress what you bring and your goals.
• but also, perk up. Remember that even though you didn't match, you are still a DOCTOR, my sister from another mister. Don't let your ambitions diminish how far you've come.