Your symptoms are suggestive of chronic sinusitis. Most of the time if colds are left untreated or partially treated, they can smolder and develop into sinus infections. You have a greater chance of developing these infections due to your lifestyle of constant travel, water intake from unknown sources, exposure to different weather,etc. The problem with sinusitis is that if it becomes chronic, then it requires surgery to cure it if antibiotics do not work. I would advise you to consult a good ENT surgeon and get a thorough checkup and of your sinuses. Immunity plays a role though we are still not sure which subset of people are prone to sinusitis. Definitely environmental factors play a role. You also need to take medications for acid reflux disease which is the commonest cause for sore throat and dry cough problems.
Next Steps
I would advise you to seek professional help from an ENT specialist