Almost certainly one of two things is going on.
1. You are consuming too few calories and your body senses that and slows down metabolism. In addition, so much calorie expenditure from exercise contributes to this. If that's the case than you need to consume more calories, and if you think thi sis the problem, then I suggest you either see a registered dietitian in your area (your doctor can refer you or check www.eatright.org). You can also check out the WebMD Diet Community:
http://exchanges.webmd.com/diet-exchange2. You are consuming more calories than you think. People can underestimate calorie intake by as much as 40%, and they can overestimate calorie expenditure by about the same amount. Although people are certain of what they consume, research is quite clear that people can underestimate. Even dietitians make mistakes. With that said, the bottom line to losing weight is to consume fewer calories than you burn, and this is true no matter how much exercise you do. Even if you run a marathon every day you will not lose weight if you consume more calories than you burn. I understand the frustration, but I can assure you that there are solutions.
You're obviously serious about losing weight and so I suggest the following:
1. Continue with exercise. It burns calories, it will keep you fit and strong, and it's the best predictor of keeping your weight off.
2. For the next week write down every single morsel of food you eat, and every ounce of beverage with calories you drink. Estimate the portion sizes as accurately as possible, and weigh and measure everything. Get a food scale and measuring cup to do it accurately.
3. Then go to the following site to figure out how many calories you are consuming
http://www.webmd.com/diet/healthtool-food-calorie-counter 4. And to this site to estimate how many calories you burn all day (called the 24-hour energy expenditure (24-hrEE)
www.webmd.com/diet/healthtool-fitness-calorie-counter
5. And here
http://www.webmd.com/diet/healthtool-metabolism-calculator to estimate your metabolic rate. Use the "Inactive" activity level for an additional cushion for underestimation of calorie intake.
If your calorie intake turns out to be wrong and you're consuming more than you think, and you know your 24-hrEE, then you can modify your intake accordingly, and/or increase exercise, so that you burn more than you consume. For instance, if you consume 1500 calories in a day and burn 1000, then you know you have to either cut back on your calories and/or increase your exercise by more than 500 to lose.
If all of this is too confusing then just continue to exercise and do #2 and #3 to get some insight into the problem.
As I already mentioned, you can post your diet-related questions to the Diet Community:
http://exchanges.webmd.com/diet-exchangeAnd you can select one of the Diet Clubs for advice and support.
http://exchanges.webmd.com/dieting-club-10-25-lbs-exchangehttp://exchanges.webmd.com/dieting-club-25-50-lbs-exchangehttp://exchanges.webmd.com/dieting-club-50-100-lbs-exchangehttp://exchanges.webmd.com/dieting-club-100-lbs-exchange You'll find pretty much everything you need to lose weight on these sites. And of course, feel free to post back to the Fitness and Exercise Community any time you like.
Take care, Rich