You can do it without getting AF first, but you need a BT done to see if your hormones levels are low. The reason you generally have to wait for AF is because your hormone levels are flat when you get AF. But if a BT shows that they are low, then there is no need for you to wait for AF to start taking it.

If the BT shows that they are elevated, you will need to wait for AF or have it induced, so that the levels are low enough to start taking it.

Hope this helps - all the best with it!