Hello XXXXXXXX: I can answer your question. The problem is the heater core is leaking. The windshield fogs up worse as the engine warms up. This is a sickening smell of hot anti freeze. You did not say what kind of vehicle that you drive. They can be simple or complex to replace. Should you like more information about this just ask.I would be glad to help.
Please click accept if this is of help. and thank you for using ask a question. Roger
Auto Mechanic
Master tech 35 yrs.exp.15yrs GM shop