Of course we here are going to be a bit biased and say "Stick with LL!" and so on, but let's put that at aside and look at the fact that you have lost 18lbs in 4 weeks. 1stone and 4lbs in only 28 days, an average of 4.5lbs each week, and you will keep losing like that each month if you stick to LL without cheating - I seriously doubt another diet like SW could say the same, in fact I know it couldn't.
When it comes to LL, and weightloss in general, you HAVE to keep the bigger picture in mind. Sure, you may have had a low loss this week, but in your first week you lost over half a stone, and you even managed to lose just over and just under 4lbs the following 2 weeks despite lapsing - and you will continue to lose that sort of weight every week IF you stick to it 100%.
This is your first low-loss week too, which we have all experienced; some more often than others. It is dissapointing, I know, but it is not something that is consistent - if anything, doing next week 100% will see you have a loss which is better than your previous 3 week's losses.
No-one said this would be easy. Lord nows, after nearly 12 months I am living testament to the ups and downs of this diet.
Social aspects, I can really relate to - I've been abstinant through Halloween, Fireworks night, Christmas, Easter, my brother's birthday, my birthday, my Dad's 50th party, numerous nights out and various meals with my brother and his fiancé/family. Every time I felt like giving in, giving up and becoming the old me again.
BUT, I used the CBT and TA we've been taught, stayed the course, and I've come through all of that with the knowledge that instead of being the awkward, sweaty, food-concerned far bloke eating more than anyone else, I've been the slimmer, more confident, more outgoing and happier person I always felt was inside me.
Of course, it's your decision, and best of luck with whatever you decide; I just urge you to give LL one more week, do it 100%, and see what happens; ultimately,
I urge you to make the decision based on what is best for you, not based on what you felt on your WI this 1 week.
I've put that in bold as that's something that I have frequently told myself over the last few months.
EDIT: Had another thought after re-reading your sig, you've had 4 weeks on LL so it stands to reason that one of those weeks has been your TOTM (unless my male mind is not calculating something right here

) and I have a sneaking suspicion that could have been this past week? Most of the ladies here have stated that it can greatly affect their losses that week, mainly due to water retention, and that the following week they have a great loss as the water is no longer retained. Just a thought
