My flu lasted 3 days. Folks here are sick with colds for weeks at a time. I think it has to do with the severe changes in weather and close quarters in Church or grocery stores. It’s normal to have 70 degree days and 30 degrees over night. We are both avid hand washers.
The flu and cold, those viruses last no more than a week. Chances of you reinfecting four times consecutively is impossible because you're immune to the first one and subsequent evolutions of that virus wouldn't be strong enough.
You would be surprised how many infections you can get, viral, bacterial, fungal and so on and it's time you sought medical advice. You will at least get blood tests that will let you know where you and your organs stand in this ailment.
Look, I was born a long time ago with a rare disease and am susceptible to weird problems (almost like autoimmune) and I am constantly amazed at what can attack the body.
I'm sorry to intrude but I care.