loss weight and exercised regular, but now lost motivation, struggling and gaining weight

First things first, don't beat yourself up about putting weight back on, you still weigh less than you did when you started! Having an operation is a huge thing to deal with physically and emotionally so be kind to yourself.
Secondly, you won't lose weight by exercising. If you reduce your calorie intake you will lose weight without exercising. If you exercise but eat too much you won't. What exercise does is keep you fit and allow you to eat more but you can lose weight without it.
I think you need to stop worrying about the high impact exercise as it sounds as though you're feeling guilty if you don't do it and this won't motivate you. Keep walking everywhere it really is good for you and concentrate on what you're eating rather than what you're doing.
Think how brilliantly you've done and congratulate yourself in not putting all the weight and more back on. You've done it before, you can do it again! Good luck