I've been on TRT for over a year and a half now and shortly after starting I started to get migraine headaches has anyone else have this happen to them or do you think it's just coincidence that it happened?

Could be a side-effect of elevated estrogen level in your blood. Ask your doctor for an "estradiol sensitive test" to see if you're converting too much T to E2. Others can probably explain it better I've been on autopilot with TRT for years.

I have often had it before castration and TRT, but since TRT I have it really seldom.

Could be you are using too much?