Hey, Pushka. It sounds to me like you simply have a very strong relaxation response to weed. I rather doubt that iron-rich food would make much of a difference in your level of sleepiness, although it's probably very good for you in other ways. If caffeine in moderation doesn't help keep you from getting sleepy, have you thought about switching the strain of weed you smoke? Indica strains tend to have more of a "narcotic" effect, whereas Sativas can be more stimulating and energizing, at least in many. That might be worth a try. Good luck!