Yes, I went through the same thing. After gaining weight due to meds, I felt hopeless about losing it. Back in college, I used to be able to develop a plan and stick to it. But when I was in my bad headspace, I couldn't start losing weight, no matter what.
What helped me was changing small habits, and then staying with the new habits, rather than going back to the old ways once I had dropped a few pounds. To be honest, changing my exercise, like a few walks a week, did not help me lose weight. The only thing that did help was changing my food intake. I started limiting my soda consumption, from two or three cans a day to one; eating out at restaurants less, from twenty times a week to ten; eating fewer junk food snackes, from six cookies to four. As you can see, my changes weren't even close to what most people consider "ideal" diets. Four cookies? Restaurants every day of the week? Soda every day? Doesn't sound like those changes would do much good. But for me it wasn't about going from slob to perfect, it was
relative changes that worked. I can keep up the habit of one soda per day far easier that I could one soda per week, or a "no soda" rule. See what I'm saying?
I then lost 20 lbs. over two years. Not a big, fast loss, but a
loss instead of a gain. Then forty-some days ago, I started counting calories and doing the things most people think of as a normal diet. Now the weight is coming off a lot more quickly, but two years ago I just wasn't ready. I made changes that I new were realistic. After making small changes over a long time, I am at last able to maintain willpower and make more drastic changes.
So my advice to you is to pick a few small changes, changes that are relatively good as opposed to perfect, and stay with those changes for a long time. After having some success with continuing new habits, you eventually will be able to make the big changes. Hopefully it won't take you two years like it did for me.
But please accept that sometimes we can't make a bunch of big changes all at once, and you might be more successful if you start small.
Hugs!