The correct option is D am having
The context refers to "now" which indicates that the action is happening at the time of speaking. This is present continuous tense. The correct form of present continuous sentences is S + am/is/are + (verb + ing) + O.
"Am having" in option D is present continuous form of the verb and is correct in the context.
"Have" does not concur with 'now'.
"Have been having" is present perfect continuous and indicates an action which began in past but may or may not have completed.
"Am not having" is negative and does not concur with the mood of the sentence.
Thus, option D is the correct answer.