Sleeping on back after 1st trimester

So I read a couple articles that stated laying on your back after the first trimester could potentially harm the baby. It apparently could cause you to lay on a blood cord stream vein thing that could cut off circulation to the baby or something?

I forgot to bring it up at my last appointment but will check it with the doctor next visit.

I’ve been avoiding sleeping on my back and now my upper ribs/sides are hurting like crazy from sleeping on them all night, even with a pregnancy pillow!

Anyone else going through something similar or have any opinions on the matter?