Having contractions dilated to 4cm an 50 percent effaced my stomach is tight hurting like cramping feeling this is my 3rd child is it labor?

Most likely: Labor can progress quickly with each new pregnancy. I would contact your OB asap and review. Probably a good idea to have someone drive you to the hospital you plan on delivering at to have an evaluation to determine if in labor. Good luck! Don't stop at a drive thru though - sips clear liquids only until you get a medical decision on your status.