Repeated lung infections with expectoration could indicate a lung disorder that makes the lungs susceptible to infections. Examples of these kinds of lung disorders include chronic bronchitis and bronchiectasions.
Chronic bronchitis can be identified via functional lung tests, blood-gas analyses and bronco-provocation tests. Microbiological examination of the phlegm can be also performed. Bronchiectasions are enlarged and inflammatory bronchi filled with infected phlegm. Bronchiectasions can be seen on an X-ray image of the chest.

Another possibility is for your symptoms is that you are experiencing decreased immunity. You can consider taking an HIV-test to exclude AIDS.