There's any number of ways to get a rotated vector. Here's one...
var dist = 2
var v1 = Vector2(10, 10)
var v2 = v1.rotated(90 * PI / 180).normalized() * dist
var v3 = v1.rotated(-90 * PI / 180).normalized() * dist
dist is the distance along the rotated vectors to project your points (X away from A in your description).
v1 is the original vector (AB in your description)
v3 are the rotated (+90 and -90 degrees) vectors, of length