I run the distance of a half marathon every sunday,during the week between 2/5 miles 4 times a week.I have 2 jobs and I lead an active life you could say,but when I'm not mobile my back starts to ache,I've tryed everthing but I can't seem to get rid,HELP!!!!! M.

Sounds as if you are overdoing it.
You are doing between 33m and 21m per week on top of an obviously busy daily schedule.Why not reduce the mileage at the weekend to say 10 miles and just do 2 5mile runs a week and spend the other "lost2 running time doing some back stretches/strengthening exercises....but don't ask me what though!!

Steady Edwina might be able to assist with stretches.

ps
Blue or Red?!

Oh dear Valley Runner - I'm currently seeing a chiropractor for my back and it makes a hug difference. It is you lower back or further up when it aches and does you back only ache after runs or could it be work/posture related as well.

If you PM you email address I'll send you some exercises to do also have a look at www.physioroom.com.

P.S. I think Steve is right maybe reduce to 3 runs a week and make sure you have rest days inbetween.

This is a good spinal twist. If you can't cross your leg underneath you can just keep it straight:
http://www.sivananda.org/teachings/asana/sptwist.html

You can also release nto your loer back by lying on your back, bring your knees to your chest, hold onto your knnes with your hands and rock gently from side to side.

I think it as something to do with posture,I am trying to run with my arms lower to see if it helps,thank you all advice is welcome and will be used. M

If the pain higher up then between the shoulders? Try and keep your shoulds relaxed and try and engage your core muscles by sucking in your tummy.