3rd injury in 2.5 years, I need some positive thoughts

I need some help to get out of a mental funk because I am starting to have thoughts of giving up creep into my brain.  I know some of you have dealt with injuries and probably have some insight.   Here's my history.  I'm 46 years old and have never been an athlete.  I've been active all my life, but always did activities like walking, hiking, backpacking, bike touring i.e. nothing competitive.  Decided to do a tri and started running summer 2005 (tri was not until the next summer).   By late October I was running around 10mpw, plus cross training and feeling great.  Plantar fasciitis struck in November 2005.  It took a trip to a sports orthopod, lots of work and time, but by May 2006 I was back to running 10mpw and feeling great.  I was running every 3rd day, swimming and biking.  I started to increase my mileage in June and the first week of July 2006 I suffered a microtear of one achilles tendon (the week I increase to 12 miles for the week).  More trips to the sports orthopod and a couple months of physical therapy and by November 2006 I was starting to run again.  My physical therapist's comment when I told him what I was doing when I got injured was "How the hell did you get injured?"  My sports orthopod's comment when I told him all I want is to be able to run 15-20mpw was "Some people just don't have the body to be able to run that much".  That much?  15-20mpw is peanuts.  And it's not like I am carrying an extra weight because I am 5'8" and weigh around 130 lbs.  I am still having achilles issues 10 months later, but I am running pain free although I have some soreness intermittantly when I am not running.  Still I have been feeling REALLY good running and have worked back to the 10-11mpw level.  I did my second tri last Sunday and felt GREAT!

So two days ago, after a swim, I am sitting on the bench in the locker room and bend over to tie my shoe.  I feel a stabbing pain in my lower back and spend the next few minutes trying not to pass out.  The stabbing pain was VERY fleeting and I had no pain or abnormal sensation in my my legs, but now the muscles in my lower back are sore, stiff and spasming.   I have never had back pain before in my life.  I had no clue that anything was wrong.  So now I am not running AGAIN!  I'm doing all the rest, NSAIDS, ice thing and today I am feeling a little bit better and will start some stretching and light activity.  I have a massage scheduled tonight too to try and release some of those spasms.

This is so frustrating.  I have discovered that I LOVE to run.  When I am not running, all I think about is the next time I can run.  Then I read threads like the current one in Triathlon talk about do you have "it".  It makes me feel like a failure.  Like I am not working hard enough at something.  I think I need a pep talk from someone who has been through injury(s) before and has successfully overcome them.  I've been pretty positive all along, but this latest episode is wearing me down.

Thanks, Diane