have you tryed nipple stimulation? if you have a breast pump, you can pump one side at a time for 15 min...rest 15 min...pump the other breast 15 min... rest 15 min... etc. don't pump both sides at once, as that can cause pit. like contractions (too strong) if you don't have a pump manual stimulation can also do the trick...you can do both sides at once for 15 min. rest 15 min, etc., and of course your dp can help with this
there are several pressure points on the body that can help, one on the inside of your leg, the roof of your mouth (thumb-sucking) and between your thumb and forefinger, and one on the foot somewhere...look on the internet for more info on these.
i've heard bad things about castor oil as well as blue and black cohosh (although there is a homeopathic remedy that uses these...colyphyllum???i think or something close to that, which i assume would be gentler than the straight stuff) anyway, they also can cause really difficult painful contrx
have you been walking as much as possible?
more mainstream approaches are sex and spicy foods.
good luck getting that labor started!