Yes, I think a lot of us would say that getting used to sleeping on your back is hard. One thing to be very careful of is pillow use - if you have a pillow under your head that tilts your neck upwards, then that is going to cause problems. I use one of those squishy little pillows filled with microbeads (you can buy them either as a crescent shape or a roll) to just give a wee bit of support under the back of my neck and fill the gap between where the back of my head touches and my shoulders touch. I also find I need a pillow under my knees. I'm not 100% sure if this is a good idea or not, but would be something to ask a physiotherapist.
The other thing to be aware of is having a good mattress (firm generally, but with a nice cushioned top). If you have an old saggy one, then sleeping on your back is probably not going to help and could cause more problems.
