I second the tip on checking both hoses going into the firewall.
That will tell you what's going on. If just a little warm, both, then it IS your engine temp.
If one is hot, the other is not, you have a clog in the hose or heater core.
If both are hot and still no heat inside, your core may be at fault or the heater flaps (doors) or controls are bad.
Both hoses should be pretty darn hot.