Hey there Fashionista84. You've already been given some great advice and support - I just wanted to add my own two cents, so to speak. A dear relative of mine is bi-polar and I can symphathize with what you are going through.
First things first: work closely with your pyschiatrist and pyschologist to find the therapies that work best for you. As with so much in life, what works for one person, does not work for another. In this arena you must be your own advocate! Finding the right meds/therapies is a challange, but keep trying ... the right ones are out there for you and when you find them they'll make a world of difference. I believe that there is a Depression Board on this site and I'm sure that the wonderful people there will be able to offer you well-informed advice and a shoulder to cry on.
As strange as this may sound I really believe that successful weight loss is about more than just losing the weight —*it's more than that —*for me anyway, it's become a journey to health - mind, body and spirit. So to take it off, and keep it off, it has got to be a lifestyle change - not just a diet/exercise program. The good thing about that is that if you have a meal, a day, a week, or heck a month, where you don't eat well or you don't exercise right and it doesn't mean you've failed. The trick is to just pick right back up where you left off - and don't beat yourself up about!
As far as practical advice goes: don't be afraid to start slow

Change one thing at a time so you're not overwhelmed and so that you don't feel deprived. Drink more water, eat more fruit, eat less junk. Baby steps. As you feel ready, add something else to it. Same with exercise - start slow, you don't have to run a marathon your first day out. Yoga is a great idea and you can try walking or swimming or bike riding or weight training or karate or whatever floats your boat ... increase intensity and duration as time goes on, but don't think that just because you didn't have a heart-pounding, muscle-stretching, sweat-drenched workout that it was a waste of time. Movement is movement and even a very little bit is better than nothing at all. Another reason to start slow with the exercise is that you don't want to burn out on it before you start to reap the rewards. Give it a couple of months - not only will it help you lose weight and build muscle but it will also be beneficial for your depression.
Love yourself, take care of yourself, make yourself and your health a priority and don't forget to "give yourself a break!"
Grace