I get ferritin done once a year, just because I'm vegan. Mine has been as low as 15, but I have ben really careful with my intake, and it has been better.

If you change your diet, it probably won't show up in three weeks time - it takes a lot longer than that to build up your stores. If you're willing, give Floradix a go - liquid herbal iron supplement OR ask your naturopath for Femax tonic, which tastes vile, but really gets results. Nettle tea is also a great uterine tonic that is high in iron.