Is it allowed to run NM wire in PVC pipe under an outdoor porch?
No. Nonmetallic sheathed cable is not allowed in wet locations.  NEC considers outdoor conduit a wet location.

You'll have to use THWN conductors, or other conductors/cables rated for wet locations. 

If you use THWN conductors, you'll be able to fit 7 conductors through 3/4" Schedule 80 PVC (Table C.9), or 9 conductors through 3/4" Schedule 40 PVC (Table C.10).