Yes it is normal. It means 2 thinghs. "your are stimulating your unit"- as Phibby said and you are verry sensitive(not a bad thing, but you need to come in control of your ejaculation).
In time you should achive
control. Clues:
KEGELS and edging.
If you don't know what those to mean go around the forum, use the search button and if you still have unclarifications teel us.