Not to disagree with Samantha, but you're not going to gain muscle quickly enough that you lose 3 lbs then gain 1 lb in the course of a week.
Its possible that your losses/gain is due to water weight - have you been eating foods that are high in sodium and/or not drinking enough water?
And it is frustrating, but try and look at the big picture

I weigh myself every day and I have to admit I do get pissed when the scale goes up a bit, but as long as I'm at a loss by the end of the week/month, I'm okay. It might be helpful to only "count" your weigh-in once a week, as opposed to every day.