Sounds like you've got two things going there.  Motivation in general.  And struggling with the pain.

Bosnpm has touched well on the motivation.  That's something I dare say every runner deals with.

I'm thinking perhaps given your age you suffer with something I don't think every runner does.  Daily pain.  I don't think every runner does, because I've met similarly driven people my age who don't.  The reason I am associating it with age is because I've run seriously at two points in my life.  Under 20, and 45 and above.  Before 20, what was pain?  Oh, sure, I had some, but nothing like what I've found to be the rule in my 40's.  I now have pain associated with running every day - and I mean every day.  I wake up in pain, I sit all day in pain, I run with pain, I go to bed with pain.  I've seen doctors about it, and have decided from those discussions I have two options;  quit running, or run and live in pain.  For 4 years now, I've chosen the latter.

That being said, it has gotten better.  I'm running everyday now.  I wasn't able to for the longest time.  I've increased my mileage enough to run a marathon last Nov under 3 hours.  But, pain is something I have to manage every day.

Things I do for pain, which may or may not help, but I do it anyway:

- self massage, regularly

- rolling regularly on a foam roller (I got a nifty one from www.tptherapy.com)

- take a proteolytic enzyme supplement (I use phy-zymes from baseline nutritionals)

- insist on a 4:1 carb/protein intake post workout (I was on accelarade but just use chocolate milk now)

- eat spinach based salads by the truckload

- eat lots of cherries

- frequently search the web for any new tips on managing DOMS

Old age, yes, it's a b**ch

Good luck.