Rob Kardashian and Blac Chyna are back on again ... or at the very least getting it on again.

Rob showed up at Chyna's doorstep last week and hasn't left.  

We showed you how they spent Father's Day ... at Disneyland with 7-month-old Dream. As we said, it didn't make a whole lot of sense for them to take an infant to a theme park she can't appreciate, so it seems liked it was more for them than the kid.

Now we've found out Rob's been there every day and every night ... going on a week. They've been socializing with friends and family with BBQ's and a pool party, and they've taken hikes together.

Chyna dropped a ton of cash on gifts for Father's Day, including a Louis Vuitton bag, a customized Dodgers hat, sneakers and white and blue roses emblazoned with an "R."

We're told this has nothing to do with a TV show or business ... they're back into each other, at least for now.