When do you know..

When do you really know you're in labor...my back and all down my legs are hurting.. Been in pain pretty much all day.. Carrying lower AND after eating even vomited.. I am 38 weeks 6 days... Monday am being induced... I cant tell if i just want baby out or if i am slowly wee bit going into labor.. monday the dr checked my cervix and i am dilated at 3 almost 4 ...thinned out and he said i could go at any time.. Altho i know some can go weeks at 3.. Thanks mommas.