I made this mistake of thinking of yoga as primarily a stretching and relaxation practice, and while it does accomplish those things, I didn't reap the full benefits until I incorporated a yoga practice (Ashtanga yoga) along with daily meditation and breath focus to help create more mindfulness, fitness and relaxation. I'm still a beginner, but it has been a huge help with my fitness and weight loss. Being more mindful about food choices and other daily choices related to weight loss and fitness has been huge for me. I say keep trying, heavy or not, and you might find something that really helps.