Good luck with the party eek. I know how you feel. Poor DS1 has only had one proper party with friends from school and I was ridiculously stressed out about how we'd entertain them and whether it would be a success (it was, thankfully!).
Someone, can't remember who now, mentioned back pain and I have this today. Really achey and also a lot of stretching pain round the front. Not that worried, but it is annoying. Spent the whole morning at a playgroup 'eco-event' in the woods. We still have snow on the ground here! Brr, just what I wanted...