Can forced air heatcause you to have constant congestion?

Possibly. Congestion is a defense mechanism, so any insult to the nasal cavity can cause some level of congestion. Heating units without some form of humidifier often dry out the air, which can lead to nasal passage irritation, and in response, congestion. So, there's a chance the heater is to blame. There may be other allergens or triggers to blame, so it's best to be evaluated in person by a doctor.