There is no reason to stress/worry too much. Without luggage you will make it to the PG flight with plenty of time. 7-8 PM is a few hours before the midnight rush at BKK so I expect the airport to be calm and no significant lines for transfer security check. It is very easy and often quick to transfer at BKK like you are going to do.
There are PG transfer counters before the escalators leading you upstairs to document and security checks so get your BP there unless you already have it on your mobile phone.
Relax - you will be fine. I would have booked that PG flight without hesitation.