Hey,
I know ((((hugs)))) can heal stress fractures, so I will send some hoping they help 
If this is so sore it stops you running, it for sure is not a mucle imbalance or trigger point that is sore. These may be reasons why you are injured, but as you say “it became too absolutely painful to run” you have damaged/inflammed/tore something in the process which is now speaking to you. If something is this angry that you cant run and even extending the hip is painful, starting a new stretching and/or strengthening program using alot of hip motion may actually aggravate the hip, so proceed with caution.
I would proceed to sports specific manual therapist (RMT, Chiro, MD) to test out the hip joint itself, then if its all clear, start functional muscle testing, then proceed to individual muscle palpation to try to narrow down the specific injured tissue. This way you can really narrow down the structure and the injury and then the proper treatment is easy!
Martin