New to this

Hello all. I am a 26 year old mommy of a five year old and an 18 month old. When I met my husband back in 2005 I had a job that kept me on my feet all day. I weighed 135 at my thinnest. Fast forward to today and I am up to 203. (I weighed myself this morning). I have a desk job and sit all day. I have reached my "enough is enough" moment. I am still wearing maternity pants from my daughter's pregnancy. I get tired easily. Our family loves to take vacations together. This year we are going to Disney World for Christmas with my inlaws who live out of state. I don't want to be the fat daughter in law who is so out of shape that walking tires her out. I have 13 weeks until our trip and I am hoping to be down 15 pounds by then.