It’s likely your cheap iron. The second you switch you’ll see a HUGE difference. even going from a no name $5 iron to a known $25 iron will make a huge step.
I’ve had good luck with the lesser expensive weller irons and the SSVT soldering station. I’m now using the Hakko FX888D, at $100 it’s not cheap, but I’ve been using the same tip for 2 years, and it’s quality and precision are amazing.
with the cheap irons I’ve used with my students over the years (ahem, looking at you sparkfun, ahem) We’ve had nothing but problems and it’s impossible to keep the tips going for more than a few days.
I also recommend that you use a copper nest instead of a wet sponge, immediately when I did that, my tips started lasting a lot longer and oxidized less.
what iron do you have?