can’t stand/walk for long periods of time

so i can’t stand for long periods of time or walk long distances, but not because i get dizzy (that is the reason occasionally tho). if i’m standing or walker fir an extended period of time usually only after like 10-15 minutes, my body will start to hurt. it’ll be tolerable at first but unless i sit down the pain will just build. i’ll also be pretty fatigued too. i was wondering if this was because of the POTS or if it’s a whole separate issue. or like am i just unfit lol. does anyone else experience this?