Pain for Months After Zoom Whitening?

I had zoom teeth whitening 14 weeks ago I am still having pain/sensitivity. Ive been back to the dentist who did the whitening (i only had 20mins as was to painful) he has given me fluoride overnight in gum guards for two weeks with no affect. He has also put a varnish on my teeth with no help! its only my top and bottom front teeth that are causing me a problem. Ive been using duraphat tooth paste since before whitening.