16yo male discomfort in lower chest while laying down. Weight in lower area feels better. Ideas?

You could just have some slight curvature to your spine. You probably need a really deep back pop. If you play sports, there's a possibility that your muscles surrounding your backbone could be pulled or overused. If it's been like that your whole life you should probably go see a doctor. I'd say a nice visit to a chiropractor would do you well.