Thanks for the advice. I do have quite a small frame, but have never had back ache before, as am used to doing lots of gym and yoga. As the aching has carried on since the weekend, im starting to think its here until the end!
The aching definitely comes and goes throughout the day, and i find its worse when im in bed at night...i have to keep turning over which seems to relieve it a bit. The hot water bottle is definitely a godsend.
I will speak to my midwife and see what she advises.