It is just 2 weeks he recovered from it, so let your body take time to replenish its store on its own. However, you need to give him proper nutritious food which includes sprouts, green leafy vegetables, fruits specially Kiwi. It will help to increase the levels.
Next Steps
Avoid panicking as to why it is not getting raised. Keep urself stress free.
Health Tips
In case of persistence of this condition get checked by a doctor.