Good job! It is really very simple what produces results. Keep in mind, outside of medical issues such as thyroid problems (stuff like this should be DOCTOR DIAGNOSED, don't assume "it must be my thyroid" and then start self-medicating for it....) is:
Diet
Training
Cardio
Recovery
-- I'd put Diet as the top, training 2nd and cardio as a 3rd. Recovery is something that supports all three of those as part of a balanced life.
The thing is that your body reflects your lifestyle. If you don't like how your body looks, then examine your lifestyle. If you eat fast food, you are bound to have some issues w/ efficient metabolism and energy because you are feeding yourself shit that your body can't process well and despite the calories, you may still be nutritionally starved (meaning the food you eat has no nutritional value you so your body can't use it for anything -- wasted calories).
Sounds like you've made some good progress. So now if you feel like you're stalled out or you want to go after a specific goal -- you may have bodyfat you want to lose - but consider that the bodyfat ratio (e.g. 18%) is a ratio of your lean muscle mass to bodyfat. If you have no muscle and have that marathon runner look, you can still have a higher bodyfat than you would expect. Even anorexics can have a higher bodyfat than you'd expect - not because they are fat, but because they don't have enough muscle. So to that end, dieting, starving down, crap loads of cardio, lots of high rep / low weight -- is all about 'burning' but not building. Eventually your body will determine that it has to burn something for energy and it may not be getting enough from a good, nutritionally sufficient diet, and it will go after your muscle. Further, because it may not be getting enough food, it will scale back the metabolic burn rate to preserve the energy sources it has (bodyfat).
People may start suggestion this or that fat burner (legal or otherwise) as well as steroids. But the first thing to understand is that those are all only SUPPLEMENTS to an already efficient, well-established and consistent DIET AND TRAINING PROGRAM. To that end - get your diet & training in order first.
It is a good exercise to lay out your daily meal plan in a food counts program like
www.fitday.com (free, easy to use) to get a REAL idea of how many calories you are eating and what macronutrient breakdown you are consuming- -- % protein , fat & carbs. Are you eating enough total cals & is your break down good? A good baseline is 40% protein / 30% carb / 30% fats.
Then lift for your goals. If you've been doing light weights for a long time, then I'd start hitting it hard - 6-8 rep range, heavy but safe weights - meaning you can keep a tight form on all reps and go for kick your ass intensity. A good core program to product a strong base and good mastery of basic moves will serve you for life - a great core strength program is the Madcow 5x5 -- check the stickies / the Training Vault sticky on the training board for links to those programs.