Hi, and welcome.
Since your tracker says that you started out at around 315, and are now about 300-I think you are doing wonderfully.
What I would like to add to this, is that the health benefits will sort of "sneak up" on you. How soon you will start to notice also depends on your diet, your exercise level, and your starting weight. I started feeling better after about 2 months into my plan-I felt stronger, slept better, etc. and then other benefits starting happening a little at a time.
With the improved breathing, if you are continuing with the cardio exercise like you have been doing...I would expect you to feel some improvement in that area in the next 15-20 pounds or so. Part of this "relief" is going to come from the exercise-actually improving your cardio health, and part of it is going to come from the actual pounds that are not weighing your body down as well. (It is much more difficult for a 300 pound woman to walk around the block than it is for a 200 pound woman taking 100 pounds less with her...) As your body starts to get lighter, you will feel more energetic, because you are not carrying so much extra weight with you doing everyday activities.
Diet is a big key, too. The calorie counting is wonderful-but it is also important to check WHAT you are eating as well. I can eat a 400 calorie breakfast-and it can be 2 Pop Tarts (and I can feel like crap in two hours) or I can have some oatmeal, an egg, and some fresh cut up fruit-and I will feel 10x better later in the day. Nutrition is a big key. If you are actually feeding your body properly, then you will feel better. It is like trying running your vehicle on gasoline, or on Coca-Cola.