Carbon monoxide alarms are expensive, but if you have gas heat or appliances in your home you really should have one. Fire extinguishers are quite expensive, too, but surely you have one of those.
Flu-like effects (such as what you’re experiencing) are a symptom of carbon monoxide poisoning. It says on Wikipedia: “Following acute poisoning, long-term sequelae often occur.” Meaning, even if the symptoms don’t improve when you leave your home, you could still have carbon monoxide poisoning.
If you take pain-relieving drugs, your pain may be relieved regardless of its cause. You may very well feel better for awhile, but your exposure to the carbon monoxide will continue and you could die or suffer serious CNS or heart damage as a result.
My advice is to get thee to a doctor and buy a carbon monoxide alarm, as a minimum.