1. I had poor eye sight, so I had to go to an eye hospital. I had my eyes examined by an eye specialist.
2. I had bad hearing, so I had to go to see an ear, nose, and throat specialist to have my ears examined.
3. I had some hearing problems, so I had to go to a otolaryngology hospital.
4. I had some cavities on my teeth, so I had to go to a dentist's to have the cavities filled with amalgam.
5. I had some problems in my body, so I had to go to a hospital to have a health checkup.
6. I went to an otolaryngology hospital to have my hearing examined. I had some hearing problems, so I had to wear a hearing aid.
(Would you check the sentences?)
All look good except for a couple of things.
In 4 -- "cavities in my teeth" (not "on")
In 6, use the present tense in the second sentence -- "have" instead of "had" in both places.