So am I made to possess months of vanity, and wearisome nights are appointed to me.
Months of vanity - comfortless misfortune. "I am made (obliged against my will) to posses" - literally, to be heir to-irony. To be heir to is usually a matter of joy; but here it is the entail of an involuntary and dismal inheritance. Months, for days, to express its long duration.
Appointed - literally, they have numbered to me; marking well the unavoidable doom assigned to him.