Weird Car Heater Problems?

I have a '95 Grand Prix GTP with 3.4L DOHC and when I start my car in the morning to warm it up, it only gets a little warm. Also when i start driving it gets a little warmer(if the fans not turned all the way up) but still not as hot as it should be. If i turn the fan all the way up it will gradually get cooler so to even keep it somewhat warm the fan can only be put at about halfway. My temperature gauge stays right where it should be and I'm loosing no coolant at all! Recently had the coolant system flushed cause i had manifold gasket replaced. Hoping its only the thermostat but if it isn't any suggestions on where to go from there?