I've taken T3s while breastfeeding, and so have friends of mine. Also, I am pregnant right now, and they suspected a kidney stone (so I have great sympathy for the pain you are going through!). I went to the hospital because the pain was so severe, and they offered a shot of morphine. I declined, because it sounded so scary, but did take the T3s, which took the edge off. More recently, as a result of severe back pain (yay, late pregnancy!) which T3s would not even touch, my doctor prescribed dilaudid, which is a stronger opiate than morphine even. Again, I was too frightened to take it, but the medical community in any case seems OK to give pregnant women drugs from the opiate family. They might also be OK for breastfeeding. Of course, none of those things are OTC and would require a visit to a doctor.
However, perhaps someone has a more natural solution? I'd be interested in hearing it, in case my own pain comes back.