M.V.
I've heard wonderful things about the Snoogle pregnancy pillow and know of some women that still cannot sleep without it. Yes, your arm pain is from the way you are sleeping at this point.
After your first pregnancy, you will show much faster and you very well might feel the baby much sooner because you will know what those little movements are. I went from about 20 weeks, to 11 weeks to 9 weeks with my 3 pregnancies.
If the ligament pain continues or gets worse, look into a pregnancy support belt. Even Target has them relatively cheap. The best lit supposed to support the belly and take some of the pressure off of all of your body parts that are normally bearing the load of the baby.