Sleeping on your left side allows for more blood flow. And do you eat before you lay down?
No it doesn't really matter what side you sleep as long as your comfortable (as well as you can be...) Define sick? Many people's heartburn/indegestion gets worse if you lay down. You can try sleeping propped up. Also try to not eat right before bed or maybe eat some crackers before bed if you usually don't eat the couple hours before bed.... your doc/midwife for suggestions too.