I know this might sound boring but.....
Get your heating boiler serviced and get a CO detector.
I lived for 2 months getting headaches etc and it was only when I got a electrical CO alarm that the reason was discovered. I Thought the thing was knackard because it went off as soon as I turned it on.
The lung irritation and snuffels is because there is alot of unburnt by products in the air which irritate you lungs and nose.