I live in Minnesota and have a 10+-year-old Tempstar NTG3100GFA1 furnace. It uses natural gas and is a split system. It also has a vanEE air exchanger and in-line humidifier with a programmable Honeywell thermostat. 1 1/2 months ago the furnace stopped working - the blower was blowing cold air and the igniter wasn't kicking in to light the burner. I turned down the thermostat to below 50 hoping it wouldn't get cold enough to kick on. Later in the day, when the temperature in the house had dropped into the upper 50's, I turned the thermostat back up. The furnace fired up, and I was able to see the flame through the little window in the furnace. Now 2 weeks ago, the furnace did the same thing. I was hoping the temperature would stay warmer, however, this is Minnesota, and right now it's getting into the mid 60's in the bedroom and it is supposed to be pretty cold tonight. I have arthritis and fibromyalgia and am extremely uncomfortable right now. Is there anything I can do to see if it is a little or a big problem?

Sounds like you have a pressure switch or limit problem. First things to check is make sure the furnace drain is not stopped up. And change your air filter.