What is wrong with my car? No coolant after?

About 2 days ago my car overheated unexpectedly for the first time when I found that my car had no water in the radiator (and reservoir as well) and very low oil. I last checked my radiator a month back and it was 3/4 full at least. My car usually goes at least 3 months without needing to add anything to coolant. I have a rear main transmission seal leak which I've known about for a while now, big job for $600+ for a 2000 honda civic and been advised by a mechanic not to even bother with it at this point since it's too costly for the value of the car. Did oil change and bleed out the radiator for at least 35 minutes same night.

Yesterday I added 50/50 to the reservoir about 3/5 of the way around 11 am. Today at about 6:40 pm I checked my reservoir and it was completely empty. I checked the radiator and it still had fluid in it. I'm assuming that it's a leak in the reservoir but my engine when I drive starts doing jerk motions when in traffic out of nowhere and it gets kind of scary at times. I noticed that when I turned off my AC that the vibrations aren't as scary, but still the same amount of frequency. I was thinking about changing the air filter and radiator cap but I feel like there could be more to it.

Any responses will be appreciated, thanks for reading and have a good day.

That car is really messed up. Needs the transmission repaired. Needs the engine repaired. You can get it back right for about $3000-$6000, but in a couple of years it will be a flop again.

Maybe you should have a mechanic check it out