It is possible it's something else causing the migraines, not related to thyroid. I apologise for this sounding like a stupid question, but are you on any meds? Sometimes the most surprising things can trigger migraines. I was put on Lamotrigine (an anti-convulsant) for trigeminal neuralgia. It is also used to treat migraines, ironically, but it actually caused them in me. Epically. I had a migraine for 6 weeks, 24/7, steadily worsening. It caused monstrous pain, light and sound sensitivity, nausea and motion sickness. The neurologist who gave me it was most surprised, because it is a headache treatment, but equally well wasn't in the least bit surprised because drugs are individual in everyone. But the point I'd like to make was that it took me about two weeks to realise that Lamotrigine was what was causing them, just by a process of elimination.
Have you changed anything, drug-wise, recently? Or even something in the house, like a fabric conditioner, or something you eat? It could be blind-siding you, coming from somewhere you are not considering because you are focused on the thyroid. If you are in bad pain you won't be thinking straight anyway. Maybe a list of everything that's changed recently might help you to spot if something else could be triggering them?
P.S. I'll also say that sometimes you develop a food sensitivity to something that was previously okay. A pain, but true!