Weight loss is NOT linear. This is how it usually goes:

Week 1- Awesome, I've lost 8 lbs and I feel wonderful, but hungry.

Week 2- Stepping it up a notch with lots of cardio! Lost 5 lbs!

Week 3- Rocking a 1200 calorie day diet with my cardio and I *only* lost 0.5 lbs! What gives??

Week 4- Cutting my calories to 1100 and doing more cardio, it's not working!

In simple terms, here's what happened here.  You lost a lot of water, and some fat. Of that 8 lbs, 7ish was water.  And what happens with water? Your body will balance it. Around week 3 you'll see "true" losses.  And sometimes that water weight comes back. It doesn't mean things are not working. It means your water balanced.

This is also why low carb works so well off the bat, and then normalizes to a regular loss per week. It's all about the water. 

 By increasing the deficit, you've created additional stress on the body. Note I didn't say "starvation mode". You're not going into starvation mode in a month.  The more stress you add to the body, the more it's going to rebel.

 You need 3 weeks of a constant deficit to know if it's working.  When the losses equal out, you'll notice the downward trend.  It may be 0.2 one week, and 3 the next.  It's often called a "whoosh".  See a much more scientific explanation here: http://www.bodyrecomposition.com/fat-loss/of-whooshes-and-squishy-fat.html

 I weigh by the week. Why? If I eat a serving of tositos scoops (my favorite!), I will gain 3+ lbs the next day.  Did I eat 10,500 extra calories in one day and gain a lb of fat? Nope! I gained water weight.  It sometimes takes 3-4 days to get off.  What if I weighed that day and saw a gain and took it to heart?  It could derail the next days eating thinking I had ruined the weeks loss.

 Your weight is going to fluctuate.  By up to 10lbs during the day, and perhaps a couple of lbs a week.  What matters is that over the course of a month, that number is going down. Maybe not every week, but overall.

Measure, measure, measure! I can't stress this enough. Especially things like olive oil, butter, peanut butter, nuts, chips, basically anything high calorie. You'll find the "cups" or "chips" listed on the package are off by 100 calories or more sometimes.  Eat the same stuff a couple of times a week, you have a recipe for disaster.  For an eye opening video, see here: https://www.youtube.com/watch?v=JVjWPclrWVY

Exercising? You might gain: No, it's not usually muscle, especially in a calorie deficit.  It's caused by swelling, extra water retention, stress on the body, etc.  It usually happens when you start exercise, or start a new routine. In my experience, it evens out after 3 weeks.  Keep going!

Muscle does not weigh more than fat: They weigh the same, muscle just takes up less space. 

Every "diet" plan works: Because all of them are based on a calorie deficit.  You don't need to cut out every single "bad food", everything in moderation.

2 lbs a week: is unrealistic unless you have a lot to lose. You didn't gain it yesterday, you're not going to lose it in a month.

Exercise doing something you love: Find something you love and do it a lot. I like Jillian Michaels videos because she's tough and it's short.  There are some moves I can't do (like jumping jacks), so I fill in other cardio I can do. It's about making something work for you.  If it doesn't work, you won't do it.

Eat your mother's lasagna: It's one meal, it isn't going to kill you.  Enjoy it and move on. Same goes for anniversary, birthday, etc. Don't stress it.  We're in this for the long haul.

 If you need someone on the internet to believe: Try Lyle McDonald, Tom Venuto, Leigh Peele, Martin Berkham.  All good people to start with.

Protein: is great for if nothing else, it helps you feel full.  Adequate protein in a calorie deficit also helps you to not lose too much lean body mass (muscle).  I find I am also much less bloated with a higher protein intake.

Take a Break!: Every 8-12 weeks you should take a break. Make it a few days or a week or two, where you eat at maintenance. For the scientific reasons why: http://www.bodyrecomposition.com/fat-loss/the-full-diet-break.html

Your body is great at adapting. It will adapt to the new low calorie level and the exercise. Your metabolism will slow down both from losing weight, and being at a deficit for so long. Taking a break will allow your body to restore your leptin and thyroid hormone levels.  You ever notice after dieting awhile your hands and feet get cold?

Anyways, 8-12 weeks is a loose suggestion.  I take a break when losing slows down a lot over a 2 week period.

I followed low calorie - 1000-1200 net after exercise, sometimes lower for 2 years. I lost 50 lbs. I didn't break, but yoyoed for another year and a half, mostly gaining weight back.  My body just needed a break.

When I finally said, "screw it!" and ate what I wanted for 2 weeks, something happened.  I gained  a lb.  I started "dieting" a week after that, and lost 3 lbs, then 2, then 1.5 a week.  Once my body realized things were good, it let some fat go.

You will gain "weight" when on a break, notice I said "weight" and not "fat".  Quite simply, more food=more volume=more weight.  My average gain was 4-7 lbs.  It all comes off after the break.  It's only food and water, not fat! You can't gain weight eating at maintenance. 

Wow, this got long! I hope this helps someone. I know I've been frustrated on my journey, and I wish I had known these things beforehand, especially about the diet break.

Cheers!