It might be a ductwork issue if your furnace is blowing hot air but your house is still cold. It's possible that your ducts are leaking or broken, allowing cold air to enter while hot air escapes. A system damper may occasionally become misaligned or come loose, unintentionally obstructing or reducing airflow.
Check your thermostat next if your ductwork checks out ok.  If your central heat is blowing hot and cold air into the house and your furnace is on all the time this could be because the fan switch on your thermostat is set to “on” rather than “auto”. If this is the case the fan will run continuously, producing both hot and cold air. The temperature in your house will stay much cooler than desired if this is the issue. Set your thermostat fan to “auto” and wait a few hours to see if the temperature improves.
It might be time to call the pros if your home feels cold to the touch and your furnace is blowing. Sometimes all your system needs to function properly again is a good tune-up. Your system may operate more efficiently if the cobwebs are removed and all of the parts are in good condition.