1996 Buick Regal my heater doesn't blow hot air

Sounds like two problems, first what does the temperature guage read? Should be halfway when warmed up. When was the thermostat changed? Usually they should be replaced every two years. As for one side being warmer than the other, the mixing door under the dash is binding, and not allowing it to close. You'll have to check under the dash to see what moves, and doesnt move as your turning the temp from warm to cold, etc.