Nipple stimulation

I’m 33 almost 34 weeks. I’m not weird I promise but I’ve always had a habit of rubbing my nipples, not to be sexual it’s just something I always do even if I don’t notice it. Kind of similar to when guys lay down when their hands in their pants. Any who my stomach does cramp after doing it almost immediately. My question is has anyone ever went into labor from nipple stimulation.