Gaining or losing a few pounds per month is not unusual because... hormones.
I fluctuate between 190 - 200 regardless of activity. I'm not trying to lose weight... yet.
I took a course through the American Fitness Professionals Association. Some tips I learned:
For those who want to lose weight, portion control is the biggest obstacle. Eat only what you need and no more. Avoid "empty calories" like alcohol, and sugary snacks which have high-calorie content but lack nutritional value.
Mild exercise is good, but remember that muscle is heavier than fat. If you start working out you may find you lose weight at first then start gaining a little. Don't panic, just keep the pace. Muscle burns calories so just keep at it and you will start losing again.
Weigh yourself no more than once a week, on the same day of the week, and at the same time. Body weight will fluctuate daily, so it is easy to get discouraged when weighing in every day. Focus more on inches instead of pounds. It doesn't matter if you gained weight (from muscle) but lost inches from your waistline. Inches lost are more important than weight lost or gained.
Hope this helps!