GoGauxGo

First let me tell you about myself...I'm currently 16, 5' 6", and 150 lbs. I got diagnosed with PCOS about 2 years ago. I get regular exercise: I take martial arts and march with a 24-lb. bass drum in my school's drumline.
I have a cycle habit when it comes to food. The cycle goes like this: I crave junk/extra food for some time (gain 10 pounds), I get sick of junk food, I omit the junk for some time(I lose weight), I miss the junk...and it repeats. I can weigh anywhere from 145-155 in a month! Each of the 2 halves of the cycle (Gain weight/lose weight) can last for different amounts of time, and not just around my period (when most of us crave junk). I follow a low-GI diet and weigh myself every day...it's just...
Ever since I made drastic changes to my diet, there are a lot of things I miss, especially sweets. So I'll sometimes sneak sweets when my mom isn't looking. I know I shouldn't be doing it...but I miss them a lot! Yeah there are some times when we'll splurge on a cake or something (as a family), but my mom doesn't know about all of those other times when I snack/pig out. (And I prefer to keep it that way.)
I grew up not wanting sweets every day, but ever since my diagnosis, some part of my mind senses the sudden limitations on what I can/can't eat and wants sweets whenever possible.
I gain weight around my stomach - my mom won't notice any drastic weight gain unless I suck it in when I'm around her. It isn't too hard...it just really sucks when certain pairs of pants don't fit or feel funny (and then feel ok during the "lose weight" part of the cycle).
So for a week I may end up smoking my allowance on junk food...I probably end up spending $10 a week! I had a realization this week that I need to break the cycle when I saw only coins in my piggy bank...no paper! Yikes.
Any advice for taking my mind off of food or getting off the cycle? Anyone else feel this way?