Had been doing a lot of intense stretching - now on left side, pain from lower trap, up neck to arms and into head all the way down to forehead gets occasional areas of mild pain. did i injure something? pressing certain areas relieves the pain too.

Sounds like it: Stretching a part of the body too far or too quickly will damage something... and thus cause pain. That's the common sense part. So, to figure out which muscle, tendon, ligament, or some combination of such, got damaged and how to help healing, one can start by seeing her primary care doctor. An Urgent Care doctor can also help. Sometimes, formal physical therapy is needed, but not always.