I always get my prenatals at Costco. They are super cheap and usually don't have additives.
Any prenatal is good but if you need a specific one then you will just have to do your homework for the ones that don't have that vitex.
I think you were confused about when you were supposed to get your period. You should have taken your pill for 3 weeks....the 4th week you would have your period, then you take the pill again and start the 4 week cycle all over again. You thought it was a week early but it was coming on time because the week you don't take pills is the week you get your period. So yes, waiting that extra week would have messed everything up.
I'm not fully aware of your story. I take it the bcp were meant to help regulate your periods and make it easier to become pregnant when the cycles were on track. The prenatal vits I've used have been the target brand, rainbow brand, and more recently a prescription brand. I thought the rainbow brand had more essential ingredients at the right mg, but caused an upset tummy sometimes. Target brand was much easier on my stomach.
on a side note If your cycles are off I'd encourage you to have your thyroid checked as well. I learned a low or high level can throw off cycles, as in my case. Good luck!!