Vania,

You could also be mildly depressed. Maybe you need a pick me up activity to stimulate you out of the doldrums. Or, a cup of coffee with the caffeine it has. Or, some probiotics to reset your gut. The food poisoning can change the gut flora such that you are not getting the nutrients you need. Have you tried upping B-12 supplements? A bad gut can reduce B-12 absorption.