Depo/periods/baby

So, I just got off the Depo birth control shot. They say it can take three to six months for it to clear from your system. I know two people who got pregnant less then a month after stopping the shots, they where on it for 4 years and the other person was on it for almost two years. My husband and I are trying to conceive I was only on the shots for two cycles which is 6 months because you only get one shot every three months. Anyways I don't know why I typed all this but how long does it take to know you are pregnant? When I was on the Depo I had no periods at all so I have no clue when I will ovulate or anything. I am just anxious and can't wait to have a baby.