Went to the doctor today...

Daniela • Mommy of a 5 year old son and a 2 month old daughter 💙💗
I'm 21 weeks and I had a couple questions for my doc. 
#1: My headaches have not gotten better and they take forever to go away with Tylenol. She prescribed my Tylenol with codeine but I'm scared to take it. I don't want it to hurt the baby. Has anyone been prescribed this and taken it? Does it help? And side effects? 
#2: I asked her about sleeping. As of lately sleeping has been really uncomfortable, I told her I can only get comfy on my back. I then asked her if sleeping in my back was totally out the window since all I hear is DONT SLEEP ON YOUR BACK DURING PREGNANCY!!! But she told me to sleep how ever is comfortable for me. She assured me sleeping on my back is OK! 😱 Has your doctor told you that you can sleep on your back?? 
Thanks! 😁