After six months under review and after an e-mail to the editor I submitted a 3-paged paper to a journal of MAA at November.
I did not get a responce from the editor until the  fifth of May so I decided to send an e-mail to the editor to ask (in a very polite way) if my paper is still under review.
But, I still did not get an answer and now I am not sure what to do.Send another e-mail?
Maybe I am wrong ,but how long should I wait to get a responce for a note which is 3 pages long?Forever?
So, my question is:
Is it appropriate to send another e-mail to the editor or should I wait?
For what it's worth, May 5 was likely in the middle of the end-of-semester rush of projects, make-up student work, writing and giving and grading final exams, meeting with students who need at least Grade X to graduate, etc. In addition to this, your email could have gotten lost in the avalanche of student and administrative emails during this time. On the other hand, presumably an editor would have weathered this many times before . . .

I suggest looking at the calendar for the college/university the editor is affiliated with, and after the spring semester has been officially over about a week, I think it would be reasonable to send another (polite) email.