The changes can be pretty drastic... or at least they can seem that way. Work on getting upwards of 128oz of water, it helps, it really does. Not just with hunger and cravings, but with fat loss, since fat is water soluble you want to give you body more water than it needs to do it's normal daily business and the extra is for the fat processing, it sounds hard, but it's really not once you start working up to it.
Second guessing is normal. Just keep reminding yourself of why you want the surgery. For me, I knew if I didn't do something, I'd end up dead sooner than later. And I'd kinda like to see my son's graduate college, get wives (or husbands of that's what they want) and maybe have kids (or adopt), I just knew I wasn't going to last going the way I was... dieting or not, it just wasn't going to be good in the long run.
Focus on your future, not your past.
Worry about the way forward, not the steps you tripped on already.
And just remember, the ONLY person you EVER need to answer to, is yourself, if at the end of the day, looking in the mirror, you are happy with the day... then no one else can tell you you were wrong.