Similar problems but i have usually always been a tummy sleeper and occasional back sleeper. i have found that since I got pregnant i have been unable to sleep on my back at all due to lower back pain.
Also found that as my pregnancy progresses the number of pillows is increasing.
Started off with one which i would use so that I was half on my side/half tummy. Added a second pillow and have that wedged at my back to support it and now sleep on fully my side with the first pillow supporting my tummy
Have added a third pillow in the last couple of weeks which goes between my knees now that all of my ligaments have started moving.
Needless to say DH has taken to sleeping in the spareroom during the working week so he can get a decent nights sleep as my restlessness and all of the pillows are pushing him out of bed and keeping him awake. But he still comes in each morning and climbs in to bed with me to give me a cuddle and say good morning to bubs and feel her moving before we get up and get ready to go to work

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Have to admit that the nights he is sleeping in another bed I am much more comfortable, can stretch out and sleep better. Even though we have a good bed that is supposed to prevent roll together I reckon it still does occur and this has been impacting on my back and joints despite all of the pillows.