Hmm, I'm not a doctor or anything..  but how are your shoes? are you wearing shoes that make your step off-balance? cross-trainers are good for running. I'm just thinking you may be stepping off-balance and it's hurting your back. Also stretch before running. That could be it also.

i agree. it sounds like a problem that might stem from over pronation. I have had similar problems and have found that buying a shoe that is specifically designed from runners that over pronate helped. You can find more information about the type of running shoe you might need at www.runnersworld.com

Agreed.  Make sure you have the correct shoes, and do the proper stretches.  Runners World as linked above has lots of great info.

I would also recommend taking it one step further by going to a running store to get your gait analyzed.  They will then recommend the correct shoes for your specific issues.

Don't ignore the pain and work through it.  I did that, and I'm still suffering 18 months later trying to reverse it.

I am the master at running injuries-- meaning I GET them ALL THE TIME (I have literally not gone longer than maybe 3 weeks straight without having some sort of really big, make-me-stop-running sort of problem)!  When I first started, I had back pain too, though I think it may have been related from an old tailbone injury from years and years ago.  Anyway, I agree with everyone: check out good shoes, STRETCH, and rest rest rest!!  Like kaffwynn, I'm currently in a state of not being able to WALK without pain (hip/leg issues, now) because on one run exactly one month ago, when I started to notice "hmm, my hip hurts" but I was toooo stubborn to stop early.  Not worth it!!

Good luck, and I hope you feel better!  Also, if it doesn't feel better SOON, go to the doctor.  Really.

There are several possible causes for lower back while running that are mostly mentioned by others already.  Pronation (Foot stike) pain is common and could be caused by several different things:

1.  improper fitting shoes or the wrong kind of shoes.

2. historical lower back injury (this could date back for years) 

3. overtraining

4. misalignment in your hips

There are just a few that I can think of right off the top of my head.  First and foremost make sure your shoes are the right one for you.  Go online and read about pronation.  Manufactures make shoes for different types of foot strikes (how your foot lands during the running stride)  figureout your 'type' and the research the approiate shoe.  You don't have to spend a lot of money - once you find the type you need go to Mervins, khols, etc and find a 'similar' shoe.  ie cushing, pronation, support, subpronation, etc...   all manufactures market their shoes  in these catagories.  I love NB other the other manufactures and can usually find my shoe for under $40.00  BTW - running shoes have a 'lifetime'  most experts suggest you switch out shoes every 300-500 miles....

In regards to a old back injury or a misalignment in your hips, get medical attention as a precausionary measure but ALSO work on core strength.  Situps, twisting exercises, etc...  these 'types' of excercises are found all over the place just do a little research.  Remember though you need to make the routine simple and fairly quick - approx 10 mins so you can fit them in EVERYDAY. 

As for overtraining - I actually mean not doing a proper cooldown after your workout/run.  You really should be walking (5-10 mins after your run), then stretching, then icing your back hips and legs. This will help your body's 'problem areas' recover between runs. (ice where the pain is.)

Still my biggest flag in your post was 'localized' contact pain which could be signs towards a bigger problem - change the shoes, ice stretch and do the core work for a few weeks if the pain doesn't go away I'd see a Dr.

Good Luck!