... of oxygen may also cause changes in your nails. Fever , which may include night sweats (heavy sweating during sleep). Digestive symptoms , such as severe abdominal (belly) pain, chronic (long-lasting) diarrhea , or constipation . Children may also have oily or loose stools. Being underweight . Muscle and joint pain. Delayed growth. Delayed puberty . Salty skin and saltier than normal sweat. Sinus infections . Infertility , especially in men. If ...