I work out on treadmill 6 days a week for 2 sessions of 45 minutes and have gained weight - why?

You need 4.0 speed and higher in order to lose the pounds

Hi Kuhlone

Have you lost inches? Are your clothes fitting a little bit better? Sometimes the scale is not very accurate because you could be gaining muscle and losing fat.  Since muscle weighs more than fat but occupies less space than fat, your scale could be stagnant but you could be losing inches especially around the hips, waist and thighs.

Nutrition

One thing everyone should know is that weight loss is almost pure mathematics which means you have to burn more calories than you are consuming. The Weight Watchers point system tries to mirror this, but the most accurate way is to make sure you are not exceeding your calories. Julie, since you are writing down everything, I want you to use the calories calculator available at http://www.foodfit.com/tools/w8calc/default.asp Use it to estimate the calories your body needs to lose weight. But reduction in calories is not enough.  You actually want to eat MORE of the right foods.  Get rid of (alcohol, highly processed/refined foods. The right foods are packaged by nature and not by the factory, which means you want to eat more of the foods that you can wash and eat such as fruits and vegetables and less of the foods that come in the boxes.

Exercise 

I'm almost certain that you need to crank up the intensity of your workouts.  If you have been doing the same nutrition, same cardio or workout for a long time with no results, you will continue to get the SAME results (not much) I wrote an article on breaking through plateaus that can point you in the right direction when it comes to changing up your workout routine.  Click on this link to read more http://www.healthcentral.com/diet-exercise/c/58426/21350/2-5-loss

Wishing you all the best