It seems that you are not eating enough. In P3, you can start gradually increasing your calories. Not eating enough calories (especially proteins) when your system has already gotten rid of the HCG may lead you to be protein-deficient. When this happens, your body will retain water and will cause the weight on the scale to go up. So increase your protein intake. Also, you might want to cut out your dairy for 3 or 4 days to see if you could be sensitive to the dairy. Hope this helps.
I had a sausage for breakfast and a cup of coffee with 2 tsp of whipped cream, grilled chicken salad for lunch(lettuce, tomatoes, cucumbers, and broccoli) with an Olive Oil and Vinegar dressing. For snacks, I had a handful of plain pork skins with chili oil. My dinner was baked chicken leg and a cup of spinach with butter.
What P3 meal did you have?