Are cravings your bodys way of telling you that you are lacking in something?

just read a Lady's question about craving chocolate and another lady answered she must be low on vit b and chocolate has vit b in so prob why she craves chocolate. I crave chocolate too, along with some other strange cravings such as ice and aerosol spray or petrol fumes, anything with chemicals in really. Of course i haven't sat sniffing the fumes but god do i want to! I now no the ice craving to be related to a low iron count which i am now on tablets for but the cravings haven't gone. i wounder if there is a reason for my smell of fumes? I'm 34 weeks pregnant btw