Also, make sure you are getting 8-10 glasses of water (that's over a gallon) of water every day.
Talk to your doc about taking something for your thyrioid disorder. If you are on any other meds, check to see if one of the side effects is weight gain.
Make sure you are getting 7-9 hours of sleep every day. When you don't get enough sleep you tend to eat more to make up for the lack of energy.
I was only about 40 lbs overweight, but I lost 35 lbs in about 6 months. Make small changes every week that you will be able to continue with for the long haul.
Definitely don't go below 1200 calories per day, or your body will go into starvation mode and start retaining fat. Be sure to do a food journal (good one online at About.com), because we often underestimate our calorie intake.
Try doing a few high intensity intervals for 30 sec to 1 min during your cardio workouts. It has been proven that intervals burn calories much faster. This will also help you to increase your speed gradually. Try a variety of different exercises. It doesn't take a person's body long to get used to a single exercise. You need to switch it up to see results - and you probably won't need a full hour of cardio six days a week. Find a cheap pedometer and try to get 10,000 steps during your regular daily activities. Take the stairs or park at the farthest parking spots from where you are going, ect.
Stick with the weight training, it takes a while, but it is one of the best ways to boost your metabolism. Don't be afraid to up your weights gradually (if you can do 2 sets of 12 repetitions on an exercise, you need to move to a higher weight); Women don't get huge muscles from weight lifting unless they are using super heavy weights or steroids. The more muscle you have, the higher your metabolism, which leads to more calories burned with every activity.
If possible invest in a session with a trainer or nutritionist to make sure you are getting a well rounded workout and diet. Don't give up your favorite foods, just watch your portion sizes and try not to eat them every day.. You can find examples of portion sizes on Prevention.com and other web sites. Don't give up even if you slack off one day (or more). Just get back on track the next day. It may take awhile, but the weight will eventually start coming off. It is different for everyone.
Read the book The Secret. Then dont try so hard. It has a chapter on weight loss. I weighed 247--now I weigh 130. Keep your chin up. Go to youtube.com search message from water. Its from the movie what the bleep do we know. Its the same exact premise as the Secret. Best Wishes!