Why Am I Gaining Weight?

Alright I started the Bowflex workout along with a yoga routine two months ago and lost 15 pounds in about 2 weeks on a 1500-1800 calorie diet. Then for four weeks I saw no results so I decided to try the P90X workout which I have been doing for the last week and a half. I have gained 10lbs of weight since I started it. I am worried because I know you are not supposed to gain muscle at this rate and if its not muscle what am I gaining back? I am still on a 1500-1800 calorie diet. I am eating an oatmeal breakfast with protein powder called the P90X Power Breakfast, a Lite Salad and Turkey sandwich during the afternoon hours and broiled chicken breast with brown rice and veggies for dinner. Throughout the day I will eat an apple if I get hungry which usually only happens once. I am also taking a multivitamin, fish oil, l-arginine and Tonalin CLA. I am a nineteen year old male with a large frame, 5’8″ tall, weighing 210lbs currently. I have 24% body fat and a 39 inch waste (down from 44″ at the start of the Bowflex workout). I also quit smoking when I started exercising and have not touched one since. I hope this is enough information for one of you to help me out.
Thanks, Brent