Bike fit / correct riding position

Pretty sure you already got a layback!!

Maybe a longer stem?

When I asked about your stretching though I was serious.

Also, carrying any kind of bag over any distance won't be doing you any favours.

Get some bottle cages on there and a hip pouch innit!

Yeah I'm 100% sure that the bag is the cause of the back pain. It hurts exactly where the bag sits on my back. I noticed that on yesterdays ride.

In this pic ths saddle is as far back as it will go on the rails, I'm not sure its even safe to be clamped where it is.

I was thinking of getting one of these : http://www.wiggle.co.uk/thomson-elite-setback-seat-post/?lang=en&curr=GBP&dest=1&utm_source=pla&utm_medium=base&utm_campaign=uk&kpid=5360417450

and also a longer stem if that didnt solve the issue.

As for stretching, I do stretch but not as often as I should. I forget quite a lot. I am going to be joining a Yoga for sports class next week though which will help I imagine