Try googling it Ngala, there is heaps of info on it, (I can't put up links) though some a bit scary sounding (more in relation to too much codeine).

I had to take a fair bit of it in this pregnancy for migraines, thankfully which settled down in the latter 2nd tri. I would have been continuously vomitting and in bed without it. All indications is that it's safe in pregnancy and I have an over cautious doctor and he still prescribed it.
I hope they settle down for you, I really know what it feels like and it's hard without being able to rely on the usual migraine drugs. My body took a while for panadeine forte to even work , I was used to taking imigran which works great but of course is unsafe in pregnancy.

Good luck!