In my experience with running injuries (plantar fasciitis, IT Band Syndrome, and achilles tendon issues), stretching has never helped. Strengthening, however, has helped me to recover from all of these things and to stay healthy.
If something is tight or inflamed, it’s usually because it’s not as strong as it should be and it’s being over stressed. You might consider cutting your mileage for a few days, but also incorporating some strengthening exercises.