You can't argue with what works to get rid of the flu/cold, but have you thought of trying something to not get them in the first place?
For someone who hasn't had either for decades, it's hard to fathom getting either as much as you do.
Just a couple of suggestions.
The first is to get a kit for checking your house for molds. They are found on the internet. The reason is mold can make you feel those same symptoms. They are easy to use. Comes as a small petri dish that you set out where you spend the most time in the house, open it up and just let it set for a certain length of time. Then put the lid back on and send it to the lab from where you bought it for the results of the test.
I did this when I was having 4, or 5 sinus infections a year. Mine came back negative for mold, but before I had thousands of dollars worth of dental work done, and eliminated a few root canals, and had all the amalgam replaced, I thought it was a good idea to go through the process of elimination for causes. https://startpage.com/do/metasearch.pl?query=home+mold+testing+kits&cat=w...
The second suggestion is that colds and flu usually enter the body through some orfice in the body like the ears, nose, mouth.
Get some Colloidal Silver. [Dq's friend "Ben" makes a good one] put it in a dropper, and spray bottle to put in your ears, spray up your nostrils, and gargle some for a period of time to see if it helps. As I recall CS kills something like 650 bacteria and viruses. Or you could just do it at the first sign of one coming on. This is what I do.