Motivation has been my down fall for years.
This time I focused hard on weight gain has given me (health issues, struggling to get out of cars and so on) I concentrate on horrible photos of me (in weight not face lol) I've taken a good look at my body and I've developed this dark patch on my stomach which came about when I hit 16st and hass something to do with gaining weight quickly.
Find motivational quotes online, I've been posting on a day since I started... I was reading the 5:2 diet book and although I'm not following the diet, a lot of what was said in it helps, buy a diary and write how big you are, weight, measurements, then write how bad you feel (in health, emotionals) why are you doing this? Why are you dieting? then every day/week write wht got easier, whats the same and everything and you'll notice the difference you feel but without logging it you will forget how bad you first felt.
Leaning on other people helps also. Don't beat yourself up if you slip up just get back on it as soon as possible (same day/next day).
Look for my diary and I'll help support you <3