I think you nailed it on the head.
Exercise and Diet!
It seems like an oversimplification but
I've been here over a decade, older than you, and age is a factor for sure.
Kids can be a factor as well, I have two, had a school teaching almost all young and often sick kids, lived in a dampish atmosphere, and was often sick.
I drastically changed my diet a few years ago and the changes have been quite obvious.
As Vera stated, the pickled foods and getting your PH in your gut is key.
Perhaps this is obvious, perhaps not.
Eating out often probably won't be helpful, even if it's so tasty, i.e. street food. I used to do that all the time my first few years, but I often felt it.
My endurance has gotten lower, it takes me a few days to recover now when riding a bike or long hike or something, that definitely something to consider.
Eat healthy, get the gut in order, do that cardio, and I bet your illnesses will get better and less, and you will feel overall better.
There is a ton of material online regarding healthy living, fasting, intermittent fasting, sleep is extremely important.