Tmi maybe... Idk (fingering problems)

Okay so here lackey when me and and my boyfriend are in bed , like and he's fingering me , I take so long to finish and he gets tired it's happened like that the past 3 times I'm not sure why , like I get so close but never finish , because I tire his arm out . And we go at it for awhile . I just do t know if there is something wrong with me or maybe I just need to try something different i don't know so any tips ?? Or advice