Dear Mr. Li,
      I'm sorry to tell you that I'm not feeling well today. I've had a headache and a cough. I didn't sleep well last night. I went to see the doctor this morning. The doctor told me I had caught a cold, and I should stay in bed for two days. So I'm afraid I can't go to school today and tomorrow. I hope I'll be all right and go back to school the day after tomorrow. Thank you.

敬爱的李老师：
    很遗憾地告诉您，我今天很难受。昨天晚上我又咳嗽，又头疼，一夜都没睡好。今天早晨我去了医院。医生说我患了感冒，并且应该卧床休息两天，所以恐怕今明两天不能去上学了。我希望我赶快好起来，后天到校上课。谢谢。

Dear Mr. Li,
     I'm afraid I can't go to school today. I've had a headache and a cough. I didn't sleep well last night. This morning I felt even worse, so I had to go to the hospital. The doctor told me to have a good rest, or it would get serious. So I would like to stay in bed for two days. I hope I will get well and go back to school as soon as possible. Thank you.

  敬爱的李老师：
    恐怕今天我不能去上学了。昨天晚上因为头疼，咳嗽，一直都没睡好觉。今天早晨更难受了，于是我不得不去了医院。医生让我好好休息，否则病情可能会加重，所以我想卧床休息两天。我希望我能尽早恢复健康回校上课。谢谢。