Maternity leave

I was wondering when I should consider maternity leave. My boss is very easy going and has already been asking me when I am wanting to go on leave but I just don't have an answer yet. Long story short, I can go on leave as early as I want and for as long as I want and my job will be there when I get back. It will not all be paid but we are financially stable and that is okay. I have already had low BP issues (dizzy, migraine headaches, change in vision, and feel like fainting) and I go this week from my blood sugar test. I am just so confused when to plan everything!