Brown blood for past 3 days

Flow started July 20 i received my first depo shot in beginning of June. Im now due for my second shot in August 30 but me and my significant other have decided to try forward baby #2 so i will not be getting my second shot. But for the past like week and a half ive had light to medium spotting and the blood has been dark for about 3 days now.Not sure if i could be pregnant or not