hmm, only thing I can think of is to 'fool' yourself by making some of your favorite recipes converted to paleo. Odd that it happens every 3 months, wondering if something triggers it?
milk cravings, try coconut milk milkshakes or almond milk
sweets, try to make some sort of flourless chocolate dessert
grain, use nuts chopped/sliced up to fool yourself that you are eating grains (a sliced almond 'oatmeal') or for that 'other' grain, try coconut bread with coconut flour http://www.maggiesnest.org/2011/03/19/recipe-coconut-flour-bread/ and then make 'zoodles' with this recipe: http://www.health-bent.com/proteins/pad-thai
In general I really don't get cravings, and if I do I find a paleo converted recipe to give myself what I want. I tend to crave specific veggies more often than normal. Edit: ok I remembered a craving, pizza, still creeps in. Try this crust recipe and add your own toppings: http://everydaypaleo.com/2010/08/04/everyday-paleo-pizza/ (recipe also can be used to make crackers)
oh and maybe this will help? http://www.marksdailyapple.com/low-carb-substitute/