Newbie needs help with space issue

I apologize in advance for bothering you, but I've not been able to get
answers from the community by searches I've done, nor have I figured out
how to post a question there.

I'm working for a gov't entity here in Mississippi and while I have
extensive Oracle and MySQL experience, as well as Linux admin experience
(which is what I was hired for), I've been given PostgreSQL DBA
responsibilities since the last DBA quit abruptly (probably due to poor
architecture and documentation here -- another thing I'm resolving).

I'm having serious space issues in a production environment and psql
commands and queries are not helping me isolate it nor determine the root
cause... possibly due to my naivete.

Would you be so kind as to give me some insight as to how to best determine
what is growing to fast and why? I have a 20G disk that recently was
increased to 40G and am now in less than 3 months almost out of space there
again.

Yours truly,
Jesse Josserand, CTO
IT Web Services, LLC <https://itwebservicesllc.com/> and
Ace Consulting Solutions, Inc. <https://aceconsultingsolutionsinc.com/>
Direct Phone: 760-566-7866
Business Phone/Fax: 855-236-5550
Owner, Sr. Consultant, Webmaster
Josserand Ace ConsultinG™ (JacG™) <https://josserandace.consulting/>
800-698-1030,
SalesRepsNow.Com <https://salesrepsnow.com/> (888-272-8885), and
World Profit Club Network Marketing Alliance
<https://worldprofitclubassociates.com/> (WPCNMA)® (800-980-8233).
All Divisions of ITWSLLC™