Studies on safety of herbs (GBS)

[298mom]

My midwife recommended the supplement/herb protocol that's from the mothering article on GBS (and she added olive leaf extract starting at 36 weeks) for reducing my colonization (I'm 34 weeks and haven't been tested yet but wanted to start the routine now).

But I haven't been able to find studies on the safety of the herbs during pregnancy, and some of them even say, "Do not take while pregnant" on the bottles.  Do midwives suggest these supposing they're safe or am I missing the research? 

Here are the ones I'm worried about:

Astragalus

Burdock root

Echinacea root

Olive leaf extract

I'm thinking I'll just use vitamin C, probiotics, and garlic (with a vaginal wash when labor starts).