I will make two 'out of the box' suggestions.But anyway, good-bye ...sigh
Firstly, can you get a friend or family member to stay the night and see if they can smell the same things you do?
Secondly, you wrote that the smell stops immediately when you switch off the gas supply or change the boiler settings. If this is accurate, it makes a physical cause related to your heating/boiler, less likely because if gas/smoke/vapour has permeated a building it is more likely to take several hours to disperse.
If you are the only person who is experiencing these smells, there are a several medical conditions and also drug side-effects that have the symptoms you are describing. See, for example
Phantom smell - Burning & Smoke - Respiratory Disorders - MedHelp
So, I suggest you see your GP and tell them that you are experiencing smells that no-one else can smell or find a cause for and that you suspect a medical cause.
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