Lady I would give your cycles a chance to regulate themselves before taking any supplements (except folic acid a few months before you plan to start trying.)
You may find, after however long you've been on the pill, that your cycles are quite different from before you took the pill, and you may not need anything to regulate them.
If you still have very irregular periods, you could see your GP, as this might be something they can help you with regardless of whether you are TTC.
Vitex/Agnus Castus is something that can be quite potent/is controversial so it certainly wouldn't be my first port of call, although I have taken it, and subsequently stopped. In terms of taking it while TTC, the advice I have read is that it is not known how safe it is to take during pregnancy, consequently some people only take it up until they ovulate, and start again if they get their period. Others take it all the time, stopping as soon as they get a BFP.
Unless you have known issues with conceiving, I personally wouldn't mess around with anything and would just let your body do it's thing for a while. Many people with irregular periods manage to conceive relatively easily, although I appreciate it makes it harder to keep track of ovulation etc if that's something you want to do.
Hope that doesn't sound patronising, and good luck!