Need to find a motivation.

I've gains about 70 lbs in the last two years. Most of it has been gained quickly so I have stretch marks all on my sides and legs now. I can't seem to motivate myself to continuously go work out or stay away from fast food. I'll last about two weeks and break down.
I've also been very stressed with school and money in general. I have also gone through depression for about a year and a half... I'm trying to figure a way out to keep myself on track and my friends don't really help much and neither does my family...