While i'm awake does lying on my back or my belly make any difference to breathing that tells if i have sleep apnea prior to sleep studu?

No: Sleep apnea is generally worse when SLEEPING on your back during certain stages of sleep when your body is essentially paralyzed. Your position of comfort while awake probably doesn't make a difference in what is happening at night unless you fall asleep on your back and stay that way. You should maintain your usual patterns prior to the sleep study to get the most accurate results.

Probably not: probably not so much while you are awake. that is why we assess for sleep apnea with an overnight sleep study to monitor your breathing while you are asleep.