There are two sorts of plateaus. One is natural and the other is man-made.
The natural plateau can last for a few days or weeks. That is where the body is doing its "thing". Various things can be happening. Fluid can be retained because of natural cycles for example: periods, unwellness or something is still sitting in plumbing (eating right or drinking lots of water will sort this out). Another natural cause is that the body is responding to new conditions that you have given it. Increased exercise can be producing muscle. Muscle weights more than fat. So although your scales show the same number - you are actually leaner and healthier. The good news is that muscles burns more calories. Short term frustration on the scales means long term success on the waist. You may find it a good idea to keep track of various body measurements to keep you motivated when the scales don't show you the entire picture. Sometimes it may be the case that your body just needs to catch its breathe for a bit because of all the changes you have rort upon it. None of these causes are long term. If it seems to be then we are likely talking about the other sort of plateau...man-made.
Man-made plateaus are caused by one of two things...not exercising and eating right. If you are not losing (or maintaining) weight long term then one of these two variables (or a keen mix of both) need attention.
As you get fit you have to work your body harder to get it to move that extra fat. When I started I was carrying an extra 87kg on me. Just moving was exercise!
Just daily living was consuming huge amounts of calories. When I started exercising just walking 10 minutes would build up a sweat - now 10 minutes isn't even a warm up. Tough hard exercise is required now to get me sweating and burning those calories at a good rate. I do 90 minutes on a exercise bike burning about 1,500 calories to keep me at a steady weight (and yep...I sweat buckets - much to my wife's horror!). You may find that exercising smarter will help you. Routine is the enemy of successful weight loss exercise. Your body will anticipate what you are doing and will regulate itself for efficiency. We don't want that...we are trying to burn off fat. So you have to keep your body guessing. One day regular speed and length, next day - go harder and longer, and the day after ease right back to a little less than your regular day.
With increase exercise what usually happens (especially when you get to the pointy end of weight loss) is that without realising it we have increased our food consumption. We are literally feeding extra to our body to make up for the extra exercise. We tend to increase snacks and potion size. A careful food diary will uncover quickly where it is going wrong (that is if you are disciplined enough...I never was good at keeping a food diary). Decide what you are going to eat before hand...and don't listen to your body when it wants extra...tell it to go eat that fat!
That's the basics covered. Hope this is helpful.