Heater issues

My situation began when my radiator cap failed and antifreeze came spraying out the top.

I replaced the radiator cap and refilled the antifreeze in the radiator. At this time the level in the reservoir was just below the max line (still within good range).

A couple of days later I noticed the heater would only blow hot air if I had been gassing it for a few minutes and as soon as my foot came off the gas the air went cold, just as cold as it is outside. Thinking the radiator must not be filling with antifreeze I took off the radiator cap and checked. Sure enough, there was no visible antifreeze inside. So I refilled the radiator and still the reservoir seemed still in good range (though it's very difficult to determine the level because it is not very see-through even with a flashlight) but it possibly may not have been. This seemed to fix the heater issue.

Well the next day the heater was doing the same thing and the temperature gauge went all the way to the red H. This time when I checked things out I noticed a leak coming from the dome where the thermostat is. I took it apart - the thermostat seemed good but the gasket was loose so I just replaced the thermostat as well as the gasket. Refilled with antifreeze again. Heater again worked good for half a day then back to the same problem. At this point I'm unsure if the leak was really fixed or not because I wasn't able to clean up much of the antifreeze on the engine so it still looks a little wet, may be more leaking, I don't know.

This time however, though the radiator appeared empty, the reservoir was full to the brim up at the cap. For tonight, I sucked out most of the antifreeze in the reservoir to just a little above the max line and didn't refill the radiator in hopes that for my morning commute the radiator pulls from the reservoir. If not and it gets hot, I'll have to pull over and put some in.

From looking online, I've seen the same issue with other Civics and have heard possible problems being a blown head gasket, the heater core or just air in the cooling system. I'll also add that from what I've witnessed my fans are coming on until the car has been stopped and idling in Park for a minute then they turn off. I'm no expert with car mechanics so before I take it somewhere and possibly pay for something I may not need I want an opinion from someone who knows more than myself.

Sorry for the lengthy story but thank you for considering my situation.