I have submitted a research paper in pure mathematics in a good (in the sense of science citation indexing) journal published by some university in USA. It has been over 3 years in the journal. In the mean-time, third round of revision (a minor revision) was submitted two and half months back. The first round of review took almost 2 years, then a minor revision of for second round of review took almost a year. The final and third revision was submitted two and half months back. The review reports were positive every time. The last time (two and half months back), the editor said that the referees will inform soon. Completing two months, I gave another polite reminder (15 days ago) about the status of the paper, but I received no reply from the editor. I understand, an editor might have been busy and might have been missed or forgot to reply. 

>If I give another follow-up email to the editor, would it be polite or the editor mind it? If I write a follow-up email, what should be the message of the email?     

Some more information: I am a graduate student and submitted my thesis. I am looking for some publication for next. So a timely referee report is important. Let me tell you that the paper is almost 30 pages paper in fundamental mathematics, that is, mostly theorems, lemmas etc, not much figures. However, in my opinion, the mathematics in the paper are not very difficult to review by an expert. 


Any advice please