Don't let it get you down, use it as motivation. Is there anything in particular you think contributed?
stay positive and you'll lose it again in no time.
I find I stick to my meal plans better when I only plan a few days ahead at a time. Sometimes when I plan the whole week, I get to Thursday and think "I really don't fancy chilli tonight" then I end up getting a takeaway or something else. So if that's something you can do, maybe give that a try? It also doesn't feel like I'm spending tons of time trying to come up with a weeks worth of breakfasts, lunches and dinners either.
Hopefully the planning helps you anyway!