Splitting and cracking of fingernails (toenails may be affected in some cases) indicates the possibility of a condition called onychoschizia. This condition needs to be diagnosed and treated by your family physician or a dermatologist (if your family doctor decides to refer you to dermatology. I routinely referred my patients to a dermatologist when I was practicing primary health care early in my career. There are some simple treatment plans for this condition but I tend advise doctors to avoid diagnosing and treating these kind of problems over the internet. If one gets the diagnosis wrong, a more serious condition may go untreated or receive the wrong treatments. Good luck Shelly. Sorry I could not help you more.
Regards, Dr. Haddox