Your spammer isn't thorough enough, it needs buttons and so.
Here is an example
Credits to Olli3

Finished Product
1: Place this declaration at the following spot.
Code:
Public Declare Function GetAsyncKeyState Lib "user32.dll" (ByVal vKey As Long) As Integer
2: Make a button, rename it to Start
Code:
On Error Resume Next
If TextBox1.Text = "" And TextBox2.Text = "" Then
MsgBox("Please place a message and interval", MsgBoxStyle.OkOnly, "Place a message and interval.")
Else
If TextBox1.Text = "" Then
MsgBox("Please place a message.", MsgBoxStyle.OkOnly, "Place a message.")
Else
If TextBox2.Text = "" Then
MsgBox("Please place an interval", MsgBoxStyle.OkOnly, "Place an interval.")
Else
Timer1.Interval = TextBox2.Text ' If you want it per seconds, make it Timer1.Enabled = Textbox2.text * 1000
Timer1.Enabled = True
End If
End If
End If
On Error Resume Next
3. Make a timer (leave it as Timer1)
Code:
SendKeys.Send(TextBox1.Text)
SendKeys.Send("{ENTER}")
4. Make a stop button and place this code in
Code:
If Timer1.Enabled = False Then
MsgBox("Spamming hasn't even started!", MsgBoxStyle.OkOnly, "Hasnt Started!")
Else
Timer1.Enabled = False
End If
The spammer itself is done
Now to add hotkeys
1. Create another timer and set its properties to enabled = true
Now double click on the timer and paste this
Code:
Dim SpammerOn As Boolean
Dim SpammerOff As Boolean
SpammerOn = GetAsyncKeyState(Keys.F2)
SpammerOff = GetAsyncKeyState(Keys.F3)
If SpammerOn = True Then
Timer1.Enabled = True
Else
If SpammerOff = True Then
Timer1.Enabled = FALSE
End If
End If

DON'T USE THE IMAGE ABOVE, IT HAS AN ERROR IN THE CODE
Hope this helps.