Isn't it obvious? What are your code doing?

1. Button pressed?

2. Yes, goto send SMS

3. Button pressed?

4. Yes, goto send SMS

5. .....

You are in an endless loop.

You may check if the button is released before sending another SMS.

Or have a timer to send every say 10minutes if the button is still pressed.

Or have a flag set in the sending SMS routine and cleared when the button is released

Or...

Ioannis