Postpartum weight?

I'm really starting to get depressed about all of the weight. I weighed 103 lbs before I got pregnant and when I delivered, I weighed 155 lbs. 4 months PP and I weigh 145 and I have all of this I guess what you would call it is baby fat? How do I tighten my belly back? My thighs and arms are big also. I've heard of a band that goes around your stomach but I'm not sure what it's called. Any suggestions on how to lose the weight?