Are you weighing yourself at the same time of day? Or was it one time in the morning, then in the afternoon and then in the evening? Under the same circumstances? That's very important. Our weight can go up easily over 5 lbs within the day just to come back down the next morning.

Choose ONE time of the day, for most folks that's early in the morning, upon waking, after using the bathroom, before eating, wearing the same clothing (or none), in the same exact spot.

I agree if you track your calories online track sodium- anytime you eat out your sodium shoots through the roof!

Also are you recording your weight somewhere ?I put mine on my calendar so I always know what I weighed on a certain day. You didn't sound too definite about when you weighed yourself,

My guess would be that the weigh in where you had lost 8lbs in 4 days was not probably reflective of actual loss. To lose 1lb of body fat requires a deficit of 3500 calories... for most people this is well over what can be created in one day. Let alone 7000 in one day, which is what you would need to actually burn 2lbs of fat in one day.

So, then, if you discard that weigh-in which was probably not accurate, the gain is not 12 but 4 lbs over a week and a half. Which is easily achievable by variation in water retention.

On the plus side, though it takes a 3500 calorie deficit to lose a pound, it also takes consuming an extra 3500 calories above what your body needs to gain a pound. Which also can't happen in a really short time.

Hope that helps.