Finding Motivation after Weight Gain!

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I started my weight loss journey November 2012, and until about a month ago I seemed to be doing fine; losing nearly 30lbs. But over the last 4-6 weeks I gradually went back into my old lifestyle. I have no idea why I should have been more motivated for a recent holiday abroad, but I just wasn't.

After coming back of holiday I stepped on the scales and low and behold I had gained 12lbs. In that short space of time. I think because before the holiday the old habits were creeping in I had gained around 2-3lbs and I was naive to think that was only water weight. (so 9-10lbs on holiday)

I just want to know how to get back into the swing of things, if there's a plan I could follow to ease my way back in?

I know I need to do this for my health but it's like I have no desire too anymore, my clothes are alot tighter before I would have never noticed how a 12lbs gain felt... let's just say its no walk in the park.

Any help or suggestions welcome.
Thanks.