For a believer in Christ, what would be the reasons for someone who has multiple illnesses over many years? Is it another trial? Discipline? There is no unrepentant sin that I know of, other than perhaps not praying about each illness daily.
While the Bible does teach that the Lord may visit us with a physical ailment as a consequence for unrepentant sin (see 1 Corinthians 11:30), we cannot assume that every illness is the result of God’s discipline or judgment. On the contrary, physical illness and weakness are a natural result of God’s curse on the earth and the natural deterioration of the body over time.
Certainly, illness is a trial in every case, and the Lord will use trials to strengthen us. Moreover, prayer is always the proper response to any trial, including illness, and the Lord may answer your prayer with healing. Nevertheless, we can never say that a particular illness was a result of a particular sin, much less that a string of illness were anything other than poor genetics or simply a particularly bad season of illness.