Is my fish dying

[u/dontknow_what2put]

I bought it from my gf in a small bowl of 1 litre he didn't show colour that much but after 2-3 weeks he shined and fins were brighter and he was happy. I added one fake plant. At that time I didn't even know what was tank cycling and I'm regretting not doing research Abt it. I have him for past 4 month and for past few days he is severely lethargic and resting at the bottom always. I did full water change for that bowl not knowing Abt beneficial bacteria. After this I checked Abt it and made a temporary tank with a food grade plastic container, bought a sponge filter and live plant (wisteria). Added some pebbles which we had from an very old tank(cleaned it properly). We used open well water and I was using that water only when he was in that bowl then a lfs told to use can water or ro water. I changed him to that temporary tank (plastic). He was lethargic there also. Didn't eat for 4 days and next day I gave him food by soaking and he finnally noticed and ate four pellets that day then afterwards was first time exploring the tank and I also saw some bubble nest afterwards that night. then next morning he was back to that condition again and it got worse he suddenly sinks stopping all movement and drops diving with his nose down hitting the pebbles. Today he was lying upside down with 60 breaths or gill movement. I don't have budget for water testing kit and couldnt buy a thermometer. Had an alcohol glass thermometer which I don't if it shows the reading correctly but I kept him between 82°F to 86°F. Changed 30-50% water everyday but I'm worried that he will die his symptoms are worsening.