Diet changes making me gain?

I have recently been told i am Gluten Intolerant, while it sucks that i will have so many restriction's i was also happy to know that i would be able to shed those stubborn 10-15 pounds ive been trying to get rid of this year. I'm about a week into my new diet and ive gone from eating nothing but pizza, white bread, kraft dinner, and a wide variety of junk, to yogurt, fresh fruits and veggies, and lean cuts of meat. my portion sizes have also been slightly reduced, not that portion control was ever an issue... anyways. instead of losing about 3 pounds in the week with my new diet and the walking ive been doing to the grocery store for fresh produce... i have instead managed to gain 10 pounds!! A friend of mine say's that the sudden 360' i did with my diet likely put my system into a kind of shock and i will gain for another two weeks before i start losing weight. I guess my question is... is this possible, has it happened to anyone else? Im also open to suggestions! Thanks :)