I took Seasonale for 5 months with about a 10 pound

weight gain. A while ago I took
Ortho-Cyclen 1/35 (which is very similar to the Seasonale) for 5 years, followed by 3 years on Depo, then a 2+ year break with a Paraguard IUD, never having gained more than a couple pounds at a time. I took the Ortho the same way as the Seasonale, but with 4 packs back-to-back so as not to have many periods.
I am now using the NuvaRing; I like it a lot. I have also returned to the size/weight I was when I started the Seasonale without conciously making any changes in my diet or activity regimens (hmm, probobly a lot of water weight).
Detoxing your body of birth control means that you are giving enough time to allow your normal horomone processes to take back over without the interference of horomones (BC). Depending on the BC used, this can take from months (pill) to as much as a couple years (Depo).