I'm not sure which oil works best for whitening, but have you tried using clay to brush your teeth? I have found that dipping my wet toothbrush into dry powdered clay and then brushing works wonders at pulling stains and toxins from teeth, it also re-mineralizes and rebuilds enamel which will help prevent new stains from forming. oil pulling + clay brushing should help remove the stains in no time, regardless of what oil you use. I use green Bentonite
and fullers earth clay, they are the only clays I have tried so I can't say which is best as the clays I use both do different things, and I prefer to use them together to get my teeth the cleanest. The fuller's earth is the most absorbent, so it would probably pull out the stains faster. I use it first and then finish up with the green bentonite, it seems to help "clean up" after the fuller's earth since it has better toxin-binding abilities.
I just had a baby 3 months ago and I know how it can be with diet etc.. All the cravings.. lol. Everything I ate made me sick during pregnancy, and now that I am breastfeeding I still can't eat the things that I normally would, even healthy things like broccoli hurt her digestive system...
I wish you luck, just be persistent and they will go away. :)