Some people might only have it happen a couple of times, others may have it throughout the first trimester and some may even have it for the majority of the pregnancy. It's nothing to be concerned about unless there is bright red blood associated with cramping and discomfort :)
Brown/light pink discharge is completely normal. It's just your body adjusting to pregnancy by discarding of any old blood, remembering that this is your first month without a cycle. It's when and if you get BRIGHT red blood that it can be concerning and should be tended to straight away.