I started ADF a while back and lost a stone and half and felt great. I was doing a lot of walking too and really toned up. Then we had a 2 week holiday and when we came back went onto 5:2. I've stuck to 5:2 but have now gained back 8lbs and haven't been walking as struggling to get time. I stopped eating sweets (was a big thing for me, I ate a LOT) about 3 months ago and thought the weight would drop off me but amazingly that has been when I've been gaining weight like crazy. I am in menopause so know I will be battling oestrogen which can make women gain but I just feel miserable. I feel fat and disgusting and can't seem to get the energy to fast more. I loved fasting before my holiday and it was easy but I've run out of steam with it. WTF can I do?
Recheck your TDEE then log your food on MFP for a week to see if you can work out where the extra calories are hiding. Drink more water as well : a pint of water every time you would otherwise think about food.
Also, if your exercise has dropped, your TDEE needs to drop (for me its a 400 calorie a day difference)