Maybe it's tied to motivation, maybe it's not. Some people just seem to bounce off the walls all day. I have always had low energy level and somewhat struggle with it. It doesn't seem to be uncommon for introverts, including infps. I do love to socialize with people I am comfortable with though so I have gone through times when even after working 9 plus hours, I can come home, jump in the shower and set off again. But only for low-key hang-outs, none of those wild parties with strangers, eek.
I am curious to hear about your general routines, how much you accomplish in a day, how much is 'normal', what you do for more energy... I do have some bad habits I need to get rid of that makes my naturally mellow energy worse. Some people gets up at six and just keeps going.