Sleeping on your back at week 20

Hi mummies, I am having trouble sleeping lately… ive always been a side sleeper but ever since im pregnant, i find comfort sleeping on my back. I find that it provides support for my back and i always almost have a goodnight sleep when i do so. However, now that im in my week 20, ive been advised to lie on my side and in particular my left side. This has resulted in aching shoulders and arms from leaning on them the entire night! I also have difficulty falling asleep on my side… Hence, would really like mummies advices on this… whether it is ok to still lie on my back since it provides more support and comfort for my body (based on what i personally feel!) ? Or is it strongly discouraged to do so (understand its not good for blood flow and my heavy body maybe pressing on some nerve) ? TIA! Btw i do use a pregnancy pillow :’)