Previous posters talking about adjustment are correct. If, for example, if the heel is tight at the bottom before the entire shoe hits the drum, it will feel spongy as the top of the shoe tries to go out to the drum. Proper adjustment is everything. I seriously doubt air is your problem.
We've had others on this board with the same symptoms, they've been given a dozen ways to bleed that never helped. Once they used the proper tool to adjust the brakes they had brakes like on a new car.
Which brings me to the next point. In several instances I've loaned my tools to them to accomplish this. However, I can't find any location information in your profile. Were you close, I'd loan you mine, and if you were close to others, like Rich, for example, he'd loan you his. Others would as well, but they need to have some idea where you are to make it practical. Enough said.