Its quite possible the paint solvents are still being cooked off, however you really need too ensure that you have good ventilation.
It sounds to me as if the air being used for combustion is in fact the normal heated room air which is being recirculated and recycled.
More and more oxygen is removed during each recycling, replaced by Carbon Dioxide so after a while the atmosphere becomes quite heady and sleep inducing.
We have a log burner located in a traditional Spanish fireplace with a metal flue pipe extending beyond the top of the chimney. Ideally we should cut a ventilation
hole in the wall at the back of the fireplace to allow combustion air in so that the room air doesn’t get recycled through the fire so often. This is not an option at the moment so whenever we have the log burner going we leave a window open.
You should also be aware that different types of logs can and will project odours into the room and some of these can be quite strong.
Take a look at http://www.stovesonline.co.uk for advice and information.
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