Are you medicated? If so, it will right itself? It's important for your wellbeing to treat this, not only for your milk supply. You must feel like utter crud on top of the usual exhaustion that comes with having a newborn. What's more, I would think that trying to treat the undersupply would be ineffective if you do not address the underlying problem.
Good luck. I am on thyroxine also and have had no issues with supply. It's just important to monitor levels nad ensure the doseage is correct.