Oh Doydie! I'm so sorry to read about your DD's dog. That is so sad!

Costochondritis can be quite painful!!! I don't know if you are able to take NSAIDs but those help quite a bit. Slow, gentle exercises as well as good posture help as well (which is sometimes so hard when the pain is so bad). Heat, ice, and a muscle rub or even Vicks vapor rub help as well. Does the NP think this is from your procedure?