You are retaining water and losing muscle.
You need to consume 20-30% of your calories as fat. If you don't have enough fat in your diet, your body goes into a "famine mode" and starts consuming muscle tissue instead. This is because fat is needed for the proper operation of your nervous system, so your body conserves it. Reducing saturated fats is a good idea, but don't avoid all fats.
It is also possible that your scale and the doctor's scale are calibrated differently. I work at a hospital, and there is about a 5 pound difference within all the medical grade scales here. You need to stick with one scale and pay more attention to the change in weight rather than the actual number. Also your weight changes throughout the day as you eat and excrete.
The only way to lose weight, get fit and stay that way is the slow way – healthy diet and regular exercise. Think long-term: wouldn't you rather get fit and stay that way for the rest of your life?
No dieting: dieting ends, a healthy diet is a lifetime of good habits. A basic healthy diet: lean meats and legumes, dark veggies, whole grains, lots of water, reduce processed carbs (soda pop is Satan!) and increase fiber. Snack on fruits and veggies instead of salt and sweets. You don’t have to count every calorie, but you should be aware of your overall intake.
It’s unrealistic to say you will never treat yourself to deliciously evil food ever again. The first time you fail becomes the excuse to quit completely. Allow yourself a moderate splurge once every two or three weeks. It’s easier to be good if you know there’s a treat in your future. Don’t buy it until you’re going to eat it – who can resist the temptation? Not me!
Exercise: you're doing great there. Don't quit! Sadly, exercise doesn’t burn enough calories to lose much weight – two miles on the treadmill equals about half of a Big Mac. But exercise is irreplaceable for a healthy heart, stamina and flexibility. That means a longer and more active lifespan.
Each body has different needs - find what works for you and stick with it. Educate yourself – anatomy and physiology is the owner’s manual for your body. There are thousands of websites with nutrition and exercise information. You can tell the good ones – they aren’t selling a quick diet fix or the Nuclear Abdominatorizer.
Don’t quit just because you fall off the wagon one or twelve times – that’s just an excuse for laziness. It took years to develop your bad habits; it will take time to change them.
Remember – your biggest obstacles are laziness and unrealistic expectations. Your best tools are perseverance and education.
Good Luck!
Some links to get you started
Nutrition
http://www.mypyramid.gov
Exercise, nutrition, and a lot more
http://www.webmd.com/