I have a small (was large) hiatus hernia, not sure which of my symptoms it causes to be honest but I've never really had the pains you describe and am told its uncommon to actually have pain from the hernia itself. Could it be acid reflux? mine sometimes permeates through to my back.
The thing with GPs is some are useless, you have to just insist. I had the exact same problem as you, they told me it was all in my mind, and they even convinced me it was! I went through so much stress trying to combat the "anxiety", none of it helping, until finally I was diagnosed with gastritis and GERD!
So don't listen to them, be insistent, and dont take no for an answer. Remember you have a legal right to a second opinion and exercise it if they refuse to check you out thoroughly. Writing off pains as "stress" is just a lazy cop out taken by many GPs.
GERD, Anxiety, Depression, Rolling Hiatus Hernia, Esophageal Hypersensitivity