Hi there! I'm just a nursing student, but I do know that stopping the medications AMA (or, against medical advice) can cause some side effects. I also take anti-depressants and they help tremendously...but when I am non-compliant with them, I have horrible side effects of nausea, headache, syncope (extreme dizziness, feeling faint), hypotension (low blood pressure)...the works!
As for the abnormal period, it could be? I would just place a call into your physician/family doctor and do a quick check! Menses aren't always regular, so it could just be an abnormal period!
Good Luck!