Sorry to hear that you are having such a horrible time! Hopefully it'll pass for you soon.
When I was pregnant with my first daughter...2003 I was given a sample of a chewable vitamin. Just like the flintstones but bigger and prenatal. I didn't like it because I don't like chewables...tums makes me gag. I do however have a few friends and family members who absolutely swore by them. They had the same problem as you...couldn't even swallow a quarter of their pill.
I forget the name but I am sure your midwife can give you more insight. I think it may come in different flavors as well.
Hope this helps!