I assume by ‘obvious’ you mean the way you are practicing the Plank and the Down Dog. Therefore, I am guessing that there must be a misalignment in these poses or a misunderstanding of how to work. Without knowing more specifics about your injury, it is very hard to give you asana suggestions. But I can give you some general guidelines for dealing with injuries.
Not long ago, I dealt with an injury. I was certain that I knew how I had hurt myself and what I needed to do to heal. But the injury kept reappearing and persisting. I had to drop all my preconceived ideas and my ego about healing my injury. I started listening to suggestions until I began to see what I needed to do. I had thought the injury was obvious, but it turned out not to be.
You might benefit from the help of another teacher, especially a more seasoned one. I would look for a senior Iyengar teacher or a teacher who specializes in yoga therapy. I would not be shy about getting more than one opinion. Go to workshops, read anatomy books. This is a good time to engage in learning all that you can about the shoulder joint in general, and your injury in particular.
I would also encourage you to go to a physical therapist. A good one will be able to diagnose your injury and give you exercises that will help you strengthen the specific areas that have been damaged or weakened. It is good that you are getting muscle work already; scar tissue can build up, and the more you can avoid that, the better.
Teaching can be a hazard. Your injury is still somewhat new, and it is vitally important that you do everything possible to avoid reinjury. You may need to back off from certain asanas, both in your practice and in your teaching. We often get hurt while teaching, because we are focused on our students and are less mindful of ourselves. Repetition of poses can also be dangerous, especially if they are done incorrectly. If we go on autopilot, we can become neglectful. Even if we know the correct alignment, we sometimes stop paying attention.
The flip side is that injuries can be great teachers, particularly if we are willing to investigate why they happened. An injury can trigger one of two reactions: Either it will cause us to give up, or it will fire us to wake up and pay attention. In the best scenario, it does the latter and becomes an opportunity for growth.
Remember that injuries are often a sign that we are out of balance, either with our understanding of the pose or with our attitude toward our practice. Injuries demand compassion, patience, and the willingness to learn from the situation. Otherwise they will reappear in one form or another.
Here, then, are some questions to contemplate: How did this injury occur? What is its root cause? Do I have incorrect information about shoulder alignment? Did I push myself too hard and not listen to my body? If so, why did I do that? What was my prime intention? Am I demonstrating too much and not paying attention to my own body?
The most important aspect of healing any injury is uncovering the root cause and not repeating it. This may be a frustrating time, but if you engage in self-reflection, the situation could turn into a great teacher and help you take your practice and teaching to the next level.
Maty Ezraty has been teaching and practicing yoga since 1985, and she founded the Yoga Works schools in Santa Monica, California. Since the sale of the school in 2003, she has lived in Hawaii with her husband, Chuck Miller. Both senior Ashtanga teachers, they lead workshops, teacher trainings, and retreats worldwide. For more information, visit http://www.chuckandmaty.com.