12 miles to bad back pain

RUN 6.1 miles in 60 mins
Walkies with dog
RUN 3 miles to work in about 30 mins
RUN 3 miles home, about 30 mins

Today the back pain was terrible. I was wearing the Camelbak and noticed that the strap under my right arm directly hits the sore spot. Time to start dx'ing this! A sign of how bad -- I took some pain killers! I NEVER do that!
-------------------------
Here's what I typed up in an email to EC, I'll put it here to I have a record of it to review:
In December my lower back started spasming. They were short lived, didn't last more than a few minutes. The spasms in the end directly correlated with stress.

And during one run in late December I started getting a focal pain on the right side at elbow height. I thought my Camelbak too tight, or the spasms pulled a muscle even though the locations differed. It stayed mostly to the right side, but every now and then would hurt across my back into the left side.

It hurt while running, but was tolerable. However it was terrible when I had to stop at a stoplight and start again. The starting again hurt! If I jogged in place, even a little bit, it helped. Pained, but tolerable.

This comes and goes, I'll have days with nothing then days where I can't bend over. 90% of the pain is still right side, with some crossing to the left at its worst. When this happens it's like a tight rubber band around my chest and I can't breathe. The pain stays between a set of ribs, which leaves me thinking I pulled an intercostal muscle, but does that explain how it comes and goes and expands to the left side sometimes? I can press on the area and not elicit pain.

If I had to take a guess, something feels out of place, as if I could just move something it would help, but I worry it's damaged somehow now. Much of the weight I've lost came from my back and torso, I'm also worried I lost strength and stability there.

Then I ask Dr Google about a "rib out of place" and find Slipping Rib Syndrome!
http://www.livestrong.com/article/11811-way-diagnose-slipping-rib-syndrome/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1150226/

Ugh. Dr Google...... why do I bother.

-------------------------------------------

Weds night was awful, lost a lot of sleep and could barely move out of bed. Rolling over, bending, anything hurt. A sharp focal pain on the right.

If I had to guess, it feels like a muscle tear or strain. But then why does the pain come and go? I've been OK for a few weeks, then this?!