So - thanks again to everyone, firstly for all your concern/interest, and secondly for all your comments and advice. it was greatfully appreciated.
i DID take it all on board and i'm sure i will be using some of the tips/ideas through the rest of the programme - however - tonight i decided to give week 4 another go and see how i got on! (sorry! personality flaw!)
i am very pleased to say there was no back ache!! - admittedly i DID slow the pace - just a wee bit though - and i was very conscious of any warning signs etc - and i WOULD have stopped if the ache kicked in again - honest!
however - because i knew the 'pattern' of the run, i just used the timer on the treadmill and went to my own music - i think this helped me loads - the time seemed to go really quicker as i sang along to the songs (in my head of course! - not quite mastered running/singing/breathing yet!!... haha) - but in general it was a good run!
i ended up finishing all sweaty and heavy legs as usual but no back ache - so all good - I'm hoping it was just a glitch/bad day at the office or something, but it did serve as a reminder that i will have to always be on guard and be careful not to push it too hard.
i am after all on a treadmill in my own house and i'm not racing anyone - slowly slowly catchy monkey as they say!
so - wee rest day tomoz and lets see what friday brings!
thanks again to everyone who posted - I'm loving the encouragement - i apologise for my personality flaw of 'not letting it beat me' ..haha ... but i WILL be careful.