I think you are nervous about something or excited about something. Shivers are reflexes; things that your body does automatically to keep you safe and healthy. Reflexes are controlled by your nervous system.
Do you drink a lot of soft drinks? Your pH level could be too low. Read about metabolic acidosis online. Get some pH testing strips that you urinate on first thing in the morning. The color that comes up reveals your general bill of health. Ideally you should be about 7.24 for good health (6.24 to 7.24 first AM urination). You may have stripped much of your trace minerals from your muscle and/or bones if you're eating junk