I am 5'7 and i currently weigh 200 pounds. it's hard for me to sleep lying on my back-it's harder to breathe. i have to lay on my side to help. why?

Sleep apnea: Sounds like you may have an upper airway obstruction that is worse when laying on your back .. This is a common cause of obstructive sleep apnea.

Sleep apnea: You may have multiple reasons for difficulty breathing, but given your excess weight I suspect you have obstructive sleep apnea and/ or some "restrictive" pulmonary process. See your MD asap as you ought not to have such issues at your young age; get counseling on weight management as you are at high risk for many other diseases ranging from diabetes to heart disease.