I know that prenatals cause weight gain. I imagine if they are formulated similarly, they sure could. I never knew that until a dr visit, I was complaining about 5lbs that I gained and couldn't lose and the dr told me it the the rx prenatals, not to worry it would go away after stopping.
Are you on any fertility meds? That can cause your weight to increase. Also, PMS can cause weight to fluctuate. I would focus most on how your clothes feel rather than a scale. Plus, drink a lot of water and avoid caffeine, which can cause bloating and water retention.