Why doesn't this BillboardGui work?

So it's suppose to create a billboardgui above the players head when they click a text button, however it's not showing up. I get no errors and it's in a local script.

local SGui = Instance.new("ScreenGui", script.Parent)

local Clickme = Instance.new("TextButton", SGui)
    Clickme.Size = UDim2.new(0,100,0,50)
    Clickme.Position = UDim2.new(0,300,0,50)
    Clickme.Text = "Click Me"

player= game.Players.LocalPlayer
char = player.Character
head = char:WaitForChild("Head") 

Clickme.MouseButton1Down:connect(function()

local Frame = Instance.new("Frame", SGui)
    Frame.Size = UDim2.new(1,500,0.5,100)
    Frame.Position = UDim2.new(0,490,0,100)
local CD = Instance.new("TextLabel", Frame)
    CD.Size = UDim2.new(0,100,0,50)
    CD.Position = UDim2.new(0,20,0,10)
    CD.Text = "Common Diseases"
local UD = Instance.new("TextLabel", Frame)
    UD.Size =  UDim2.new(0,100,0,50)
    UD.Position = UDim2.new(0,150,0,10)
    UD.Text = "Uncommon Diseases"
local RD = Instance.new("TextLabel", Frame)
    RD.Size = UDim2.new(0,100,0,50)
    RD.Position = UDim2.new(0,270,0,10)
    RD.Text = "Rare Diseases"
local URD = Instance.new("TextLabel", Frame)
    URD.Size = UDim2.new(0,100,0,50)
    URD.Position = UDim2.new(0,390,0,10)
    URD.Text = "Ultra Rare Diseases"
----------------------------------------------------------- Labels ^
local Stress = Instance.new("TextButton", Frame)    
    Stress.Size =  UDim2.new(0,70,0,50)
    Stress.Position = UDim2.new(0,20,0.1,30)
    Stress.Text = "Stress"
Stress.MouseButton1Down:connect(function()
    local gui = Instance.new("BillboardGui",char)               <----this area of the script
    gui.Adornee = head
    gui.Size = UDim2.new(0,100,0,50)
    local frame1 = Instance.new("Frame", gui)
    local stress1 = Instance.new("TextLabel", frame1)
        stress1.Text = "Stress"
    SGui:Destroy()
end)
-------------------------------------------------------------

local GallStones = Instance.new("TextButton", Frame)
    GallStones.Size = UDim2.new(0,70,0,50)
    GallStones.Position = UDim2.new(0,20,0.23,30)
    GallStones.Text = "GallStones"
GallStones.MouseButton1Down:connect(function()
    SGui:Destroy()
end)
-------------------------------------------------------------
local Appendicitis = Instance.new("TextButton", Frame)


end)

You haven't given the BillboardGui's descendants a size - You need to.