My child has has symptoms of fifth disease more than once, is this a sign of another under lining issue?

Probably not. Many viruses can cause symptoms very similar to fifth disease (fever, red cheeks, reticulated rash), so getting that constellation of symptoms more than once is not normally a significant issue. If it happens over and over, though, there might be something more significant going on, and you should see your doctor or a dermatologist for a thorough exam.