Been 11 months of nothing and just starting to notice? I’d say it’s unrelated. But this isn’t a doctor subreddit so don’t quote me on it. Also if your windows are down I would doubt it even more. Those symptoms aren’t common carbon monoxide poisoning symptoms or carbon dioxide poisoning unless you are light headed, nauseous, confused, or increased heart rate I wouldn’t put my money on it. If you are that concerned just buy a piece of exhaust pipe and some clamps and route it out the back of the car. As the car moves the air running underneath would help blow any CO or CO2 away from seeping into the cabin but if you are stopped and idling a lot then it would deep into the cabin much more. In conclusion, ask a doctor and fix your exhaust (fellow hypochondriac).
Considering installing 4 wheel drive on a Camry is damn near impossible for a regular person to do, but a new car.