I think they just help regulate hormones and improve how the system works. The agnus works on the pituitary gland from what I've read. This is from a quick google:
How Supplements Can Help
Chasteberry, also known as vitex/ agnus castus, can help stimulate ovulation and is especially helpful if infertility is due to irregular ovulation. This herb appears to stimulate production of the female hormone progesterone and suppress production of the lactation hormone prolactin, creating a hormonal environment more conducive to ovulation. Chasteberry should be taken on those days each month when you’re not menstruating and stopped altogether if conception occurs.
The B vitamins play a key role in reproductive health and also in early fetal development; folic acid, especially, can prevent certain birth defects. Experts recommend that women trying to conceive take a vitamin B complex supplement that contains vitamin B12, biotin, folic acid, and all other B vitamins, plus extra vitamin B6.
CoQ10 is a popular supplement for women seeking to improve their fertility. It may help to boost the function of eggs by helping their mitochondria to produce energy.
No proven studies on any of them really- some small scale trials but generally they don't have side effects unless you have underlying conditions or meds that might react. I'm happy even if it just has a placebo effect!
Reading about the b vits I'm going to stop my folic acid as I think it's covered in the complex anyway then take it alone if I did get pregnant.