When I was a in college, I contracted the Type A
flu, and it was like it just never went away. It was really bad
for about 6 months (I felt like I straight up had the flu), then my symptoms slowly disappeared over the next 1-2 years. To this day, I don't actually know what was wrong with me, but I was diagnosed with chronic fatigue syndrome, among other things. Like you, I was very active before the onset of my illness.