Advice for a beginner

Hi, I am a very new adult swimmer, having started learning freestyle in April. I can swim breaststroke well enough to not stop for about 250 yards. But Freestyle really kicks my butt, and after 3 months of practicing everyday, I still cannot do 50 yards non-stop. I can start out breathing every 4 strokes, but halfway through the first 25 yards, I am out of breath and breathing every other stroke. By the time I get through the first 25 yards, I'm practically hyperventilating, and need a good minute to catch my breath. I have asthma, but it's only the freestyle that kills me. Does my body weight have a lot to do with this? (I'm overweight and I'm trying to lose it, and have been swimming 7 days a week, and weight-training 3 days a week) The coaches/instructors I've worked with all say that I have good form in the water for someone who has only just learned the stroke (of course there are things I need to improve on), and that I will improve over time. But it is SO frustrating to not be able to see progress in this area. Any advice besides being patient and keep swimming??? I would so appreciate it! Thanks, Tina