Will doing weights make you gain weight?

i started last week trying to start a more healthy lifestyle starting over this summer. i was going to lead a more healthy diet (nothing low carbs or anything, just doing the right serving sizes and the right amounts of the right food groups & so far i've stuck to it), doing cardio, and doing some weight lifting. i figured after the first week i'd lose at least 1-2 pounds. but instead i gained 3. should i be disappointed, or is this just muscle from the weights? i mean i haven't done any living since basketball season, and that was about 5 months ago.