it looks like you are getting a ton of (good) advice ..
i spent half my years with under developed negatives they are a pain to print.
when i enlarge i start off with the lens wide open to focus, and then stop down 3 stops,
whether it is true or not i heard years back that an enlarger lens is optimized about that aperture ...

what developer are you using to print ?
go with something plain vanilla like dektol, it has been around for decades and works well.
dilute 1:1
use fresh developer and use fresh paper
be generous with your test strips so you see what is going on ...
make sure you agitate your print in the developer ...
and notice when your image starts to appear
with rc paper usually around 20seconds is a good sign fb it is 45 ...
make sure you develop it for 2mins ...