Will a hernia affect breathing when running?

It is possible: Depending an the site location of the hernia and if it is reducible may affect breathing. Hernias that are not reducible usually cause pain and discomfort that can affect breathing.

Possibly: What type of hernia? Hiatal, incisional or inguinal. If the hernia bulges out while running and causes pain, this could cause a feeling of shortness of breath, but is unlikely. At age of thirty, cardiac disease is unlikely but possible. You may have exertional asthma. You should see your physician.