Personally, I'm someone who has avoided the traditional medical route for galbladder issues. Although, for me, pain doesn't typically last as long as you're describing. I usually get pain starting around 8-10pm, and goes away by 5 or 6am (reliably). The "attacks" I get are pretty infrequent - maybe just 2-4 per year. My last attack was almost a year ago, and I've somehow never had one while being pregnant.
My FIL found a remedy that worked really well for me, stopped the last attack in its tracks (and may have been the reason I haven't had any more for such a long time). Thought I'd share it, in case it's something you want to look into:
Mix 5 drops of grapefruit oil in 2 TBSP of olive oil. Rub over the gall bladder and liver area. Cover with a warm, moist wash rag. Cover that with plastic wrap. Put a heating pad on top if it all for one hour. Should pass any stones that are present (assuming they're small enough).
Going to the ER is totally your choice, and if the pain becomes excruciating, it may be in your best interest, but just be warned that it's most likely that they'll recommend removing your gall bladder, even if this is your first attack, and there's not really much they can do to help you in the meantime, aside from trying painkillers (and since you're pregnant, I doubt that would be much more than tylenol!). I would *personally* try to ride it out, and if it concerns you, have it checked out by a doctor as soon as you can to decide on a course of action.
Good luck.... I'm sorry you're dealing with it at all!!