It is true that sometimes journal editors need reminders from authors. Often they are so busy that they do forget to follow up with reviewers. Since you need the publication for your graduation, it is a good idea to send reminders to the journal from time to time.
Unfortunately, journal evaluation processes are in general rather slow, especially for high profile multidisciplinary journals, as they receive a large number of submissions. However, in your case, the journal has generally been responsive and has taken some action each time you sent a reminder. This shows that they understand your problem and are trying to expedite the process. While I can understand that you are in a hurry, you must remember that journal editors and reviewers are also busy people and they are catering to many other submissions as well, and other authors must also be sending reminders asking them to speed up the process.
Thus, while you should definitely continue following up with them, you should not vent your irritation. The most important thing in communicating with a journal is politeness. You should be polite and courteous in your emails at all times. In fact, rather than venting your irritation, you can perhaps, show the urgency of the situation. Tell them that you need the paper for your graduation, mention the date by which you need it, express your anxiety and request them to expedite the process as far as possible. Politeness will, I am sure, work much better than anger or irritation.