Письмо другу который болеет болезнью have a headache have a stomachache have an earache have a sore throat have sore eyes have a high fever have a toothache feel exhausted

Если я правильно поняла, то нужно выбрать одну из болезней? Если нет, могу обо всех написать потом. Сейчас пока только одну.

Hi, David.
I heard, that you feels awful, because you have a stomachache. I think, it can be poisoning. But what it can be? You felt bad yourself after we had a pizza in cafe yesterday. I am very worried about you. You have to be treated. 
With best wishes, your friend.