Stamina goes negative when I wrote code not to?

My stamina script is going haywire, and I can't find my error so I can't learn from my mistakes, Can you guys help me?

RunService.RenderStepped:Connect(function()
    local maxstamina = 9
    local StartingStamina = 0

    print(timeyouahavebeenrunning)
    if Userinputservice:IsKeyDown(Enum.KeyCode.LeftShift) and humanoid.MoveDirection.Magnitude > 0  and Debounce == true then


        if  timeyouahavebeenrunning >= maxstamina then
                local Debounce = false
        else
            humanoid.WalkSpeed = 23
            camera.FieldOfView = 80
            RunService.RenderStepped:Connect(RunningEffect)
            while wait(1) do

                timeyouahavebeenrunning = timeyouahavebeenrunning + 1
                if  timeyouahavebeenrunning >= maxstamina then
                    break

                end
            end
        end
    else
        if timeyouahavebeenrunning <= StartingStamina then
            local Debouce = true
        else
            humanoid.WalkSpeed = 16
            camera.FieldOfView = 70
            RunService.RenderStepped:Connect(updateBobbleEffect)
            if timeyouahavebeenrunning < maxstamina then
                repeat
                    wait(1)
                    timeyouahavebeenrunning = timeyouahavebeenrunning - 1
                until humanoid.MoveDirection.Magnitude > 0 and Userinputservice:IsKeyDown(Enum.KeyCode.LeftShift)

                if humanoid.MoveDirection.Magnitude > 0 and Userinputservice:IsKeyDown(Enum.KeyCode.LeftShift) then
                    local Debounce = true
                end

            else
                while wait(1) do
                    timeyouahavebeenrunning = timeyouahavebeenrunning - 1
                    if  timeyouahavebeenrunning <= StartingStamina then
                        local Debounce = true
                        break

                    end
                end

            end
        end

    end
end)