ttc after depo when should we start

me and my husband our trying for our fourth child and were hoping for a baby girl we have three boys well anyways I was on the depo shot for about 2 years my last shot was in April of 2007 and I have had two periods as of this month and one in December so I am wondering when should we try we started to try after my first period in this month and though and behold I start some what of a period yesterday well the reason I say somewhat is because I am only spotting old stuff and tonight its darker so I know its got to be a period. I am not happy either but oh well I guess my body just isn’t ready just right now and I was wondering is it true that the deposhot can make you be unfertile a friend of mine heard that from someone and she told me that so I am wondering thank you crissy