backache during thurday running

I had back ache during this morning running.
I think when I got speed up yesterday, my back was unconfortable and got off balance.
I need to fix it asap. Insted of taking a break tomorrow, doing yoga and stretching something.

today's efforts:
mil: 9k
time: 50m58s
avg HR: 140-72%
avg Speed: 8.2km/h
calories: 421kcal
beginning time: 7:10am
location: Inokashira Park
weekly mileage: 42.5km