Add Controls dynamicly

Hello,
I have a question. I want to make a plattform, where people can create their own sites. For this I make pre build controls. When the user opens the site, he can first add a control with a button and then he can add in the control some other thinks (like a new textbox), but when he presses the add button for the textbox, then the site starts from beginning. What I do wrong? Here are my snippets.:
this is the one from my custom control:

public void createsinglechoiceforpreview() { TextBox tb = new TextBox(); tb.Text = "q"; TextBox tb2 = new TextBox(); tb2.Text = "q"; Button b = new Button(); b.Text = "add new."; b.Click += b_Click; this.Controls.Add(tb); this.Controls.Add(b); this.Controls.Add(tb2); ...