Advice to stop baby fever?

I'm 20, my fiance is 22 (we're both almost 21 and 23). We have a 5-month-old son, and for the life of me I can't help but want another baby. I keep trying to remind myself how hard it was waking up all the time at night, how much I hated being pregnant, how bad childbirth hurt, I'm trying everything and I just really want another baby.

We aren't using condoms or birth control, I'm tracking my cycle as bc, so I know in the end it'll probably happen sooner than we want, but I can't help but want to actually ttc. My fiance obviously knows I can get pregnant is okay if it happens, but we've discussed it and don't want to ttc until I graduate college.

Things are finally coming together for us and I think we'd be okay, but I still don't think we're in a position to have another baby yet and he would rather wait to have another too. Advice? Anything please?