You're on P2 and gaining? What are you eating, exactly and specifically? How much liquid are you drinking? How long was P2 for you?
I did gain about 1 lb my last couple days of R1P2, then lost 1.5 lbs during the first 24 of the 72 hours, then gained half of it back before starting P3. I think some fluctuation is normal.
I have been rock solid stable in P3 and P4 and during planned interruptions, so not everyone gains weight after the first week.