When do I test?

So my AF is due on 5th and for the past 3 days I have taken pregnancy tests but received the dreaded BFN :-( Am I testing too way or is it just not my month again? Been TRC for 5 months now. I'm 30 and think that may have something to do with it. I was on the depo injection for 12 years too which I don't think helps. Anyone else had trouble after being on the injection so long. Baby dust to all xx