37 weeks pregnant , 2 cent.dilated & 90% effaced also the babies head is really low and i feel pressure and period like cramps, wen will i go into labor?

Possible labor: If you are having those "cramps" or better say contractions very frequently( especially every 5-10 mins) it is time to get checked for progression. We cannot determine with certainty exactly at what point you will be in active labor since this varies from person to person. If you are having pain as often mentioned call your OB provider.