Why does my chest ache when i lie on my side?

Multiple causes: There could be multiple causes.If there was any trauma to the side of the chest that aches it could be that pressure on that side causes the ache to increase. If you have a really bad flu and there is fluid in the lungs then that could cause the chest to ache. Some people with very bad heartburn from acid reflux could have chest ache. I would advise you see your doctor to help determine the cause

Need neck and hip: support. If either isn't present, you're putting too much pressure on your rib cage that shouldn't otherwise be there and your entire chest. When on your side your neck should remain in complete neutral position w/ your spine and lower back. So no torsional vector forces are placed on your body while you sleep. Get proper cervical support pillow for your neck.May need pillow top mattress pad too.