When I was preggo with my ds and had a st I took source natural brand grape fruit seed extract(I get it from vitacost.com),and sodium ascorbate powder(3 pounds from vitaglo.com).
Worked well for me.
Oh, by the way, for anyone who is pregnant and battling a sore throat, I gargled with Listerine (the old-fashioned kind, not the flavored), and it totally helped. It made my throat feel much better for about a half hour, but made a difference over all too. Within a day or two my sore throat was gone.