Why is my heat so bad

#1
So I recently bought a 98 corolla and the heat is terrible, I’ve recplaced my thermostat, bled the system with one of those radiator spill proof funnels ( kept the car gunning for about 30 mins or so) it didn’t take that much coolant, maybe a little bit. Still no heat. So then I thought to flush the heater core, a little bit of crap came out and then water was flowing fine through both hoses. Then I bled the system again. Still no heat. I’m thinking about getting a lower temp thromostat but I really don’t know what the problem is, any help would be appreciated.
Thanks
 
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