recurrent pneumonia for years, doctors can't explain it

I'm in my 30s, female, and pretty much healthy except for this recurring problem. When I was 7 I got pneumonia for the first time, and ever since then I get sick several times a year. As a kid and young adult we didn't have health insurance, so I rarely got an x-ray diagnosis of pneumonia—usually they'd just give me antibiotics and send me away. Now as an adult I finally have good health insurance and am seeing the same doctor regularly. I've just been diagnosed with pneumonia for the 3rd time this year, the 6th time in 2 years, confirmed with an x-ray. Each time I need antibiotics, sometimes two rounds of antibiotics, to clear it. 

- In the past year I've had 2 lung CTs while healthy, all normal.
- I've done tests for asthma, and they came back negative.
- I just had a cardiac MRI which showed mild pericarditis, but like I said I have pneumonia so, shrug.
- I had an upper GI scope recently which showed a small hernia in my esophagus, but it's not seriously enough to cause sufficient aspiration to give me pneumonia every 4 months like this. Also, I frequently cough until I vomit, so I think it's more likely that 30 years of regular pneumonia have caused the hernia.
- I've been tested for allergies and celiac, I have none. 

- Bloodwork for standard auto-immune and immune deficiency conditions is all negative.

I'm sick of being sick, but there seems to be nothing to do about it. Open to any ideas or suggestions. Thanks!