[SOLVED] Tell if a user is holding down a key then make the players speed faster if they are?

I've been trying to make it so if the player continues to hold down left shift, there speed will continuously increase. Just can't seem to get it to work. If I hold down left shift the playerSprintSpeed stays the same, even though when i'm printing the speed it goes up. I'm a total noob when it comes to roblox scripting so any help is appreciated. Thanks!

local player = game:GetService("Players").LocalPlayer
local character = player.Character
local UserInputService = game:GetService("UserInputService")
local defaultSpeed = 16
local leftShift = Enum.KeyCode.LeftShift
local leftShiftDown = false
local playerSprintSpeed = 16

UserInputService.InputBegan:Connect(function(key)
    if key.KeyCode == leftShift then
        character.Humanoid.WalkSpeed = playerSprintSpeed
        leftShiftDown = true
    end
end)

UserInputService.InputEnded:Connect(function(key)
    if key.KeyCode == leftShift then
        character.Humanoid.WalkSpeed = defaultSpeed
        print(character.Humanoid.WalkSpeed)
    end
end)

while wait() do
    if leftShiftDown then
        print("yes...")
        playerSprintSpeed = playerSprintSpeed + 1
        print(playerSprintSpeed)
    else
        print("no...")
    end
end