Could somebody explain wht i should only sleep on my side please.....

[nobodysfool]

I am 12 weeks pg and am already having pain in my hips.
I am most comfortable slleping on my back or tummy at the moment bit was told by a well meaning lady at mother and toddler group that i should only lay on my side during pregnancy.
I remember with my 1st pregnancy i slept on my side towards the end.
Does anybody know why i should only sleep on my side?

About SPD this early, it was my first sign! I had the most terrible SI pain and my walking has slowly slowed down. Im only 10 weeks.

This is grim reading about SPD. I had it last time from about 30 weeks, I haven't got it this time at 20 weeks, but when I walk for a fairly long time, I get that familiar period painy ache which was how it started last time. Do any of you have children already? Are you advised to not pick them up?