Hi there! Welcome to the Babywhisperer forums!
The short answer to your questions is that your LO is too young to start pu/pd. Three months is the absolute youngest age at which Tracy recommended using pu/pd, and often it's better to wait until four months.
So, what to do in the meantime . . .
Here's a link to an FAQ about the age range for pu/pd that contains within it some links to more FAQs about how to sleep train an infant younger than 3-4 months.
https://babywhispererforums.com/index.php?topic=121330.0 The main methods are shush-pat and, if you need to get rid of a prop, gradual removal.
You might also try wake-to-sleep which is described here:
https://babywhispererforums.com/index.php?topic=121269.0Is your LO sleeping well at night? If so, you may just want to roll with the short naps for now and work on them more specifically if it seems like they are causing a problem. Some LOs are just biologically short nappers and, since your LO wakes happy from his short naps, this may be the case for him.
Finally, sometimes a short nap is a sign that LO needs either more or less A time in his routine--that he's not tired enough to sleep through a full nap or that he's so tried he's hopped up on adrenaline and can't stay asleep. Overtirede babies tend to wake upset. He's probably too young to move to a four hour routine, but you could try adding 5-10 minutes to his normal amount of A time every 3 days or so for a bit and see if increasing A time just a bit causes him to be tired enough to nap longer.
Okay, that's a lot of options, I know, so I hope not too overwhelming. If you post what your LOs typical EASY looks like, others wiser than I am at dealing with this age may be able to chime in as well with ideas for how to tweak to get longer naps.