Everyone suffers respiratory tract infections from time to time - usually viral and self-limiting. Some people have more frequent infections prompting the need to investigate for a cause.
Causes of more frequent respiratory infection can include chronic bronchitis, airway damage known as bronchiectasis, aspiration from reflux disease or hiatus hernia, and weakness of the immune system. Sometimes asthma can present in an adult with symptoms that are mistaken for recurrent infections.
Investigation will be guided by your story and the findings on clinical examination. They might include assessment of your respiratory function, x-rays, CT scans, blood investigations, and other specialised tests.