"I am reading a book next to the lamp."
Translation:Lambanın yanında kitap okuyorum.
You missed an important detail: this change of consonants only happens when words (not just nouns) are ending on certain consonants. İt is applied on words ending on k, t, ç, p (memorized by the word ketçap). The changes are k -> ğ, t -> d, ç -> c, p -> b. Examples: tavuk -> tavuğu, kağıt -> kağıdı, ilaç -> ilacı, kitap -> kitabı. Finally, you just didn't spell lamba correctly :)