I never understand why pediatricians are reluctant to refer children to early intervention. There are 0-3 programs in all 50 states, and they are designed to meet the needs of late talkers, and other kids with developmental delays.
I would definitely seek a speech and language assessment now, rather than wait. If speech therapy isn't recommended, really, what harm has it done? The assessment is play-based, so your little one should enjoy it, and if there is a need for therapy, the earlier the better, in my estimation. Your post definitely raised some red flags for me--the regression of language, 4 months without speech, and the perfectionism may really be a challenge for your little guy.
Goood Luck mama!
paige, adoptive mama to Elliott