Weight gain on Remeron..new Med hassles or Depression?

I have been on Remeron (Mirtazapine) for three months now and although I feel it is working great for depression and anxiety, I had to get weighed, blood pressure checked, etc before my Psychiatrist appointment and I have gained 5.8 pounds.  I am already 30 pounds overweight, and that really discouraged me.  Other than an increased appetite (mostly around that time of month) - I have no other side effects on Remeron.  I am not quite sure what to do, I really do not want to put on any more weight.  I try to walk and exercise, but the weight isn't coming off.  I have heard off of label uses that is also prescribed for people with eating disorders, and I definately don't have that.  Not quite sure what to do, I don't want to be depressed again, so coming off meds isn't a choice, as I have had clinical depression my whole life.  I don't really want to try any other medication right now..as I don't want to go through the side effects.  I had a terrible time when I was on Zoloft, Prozac, Cymbalta (where I had to be hospitalized from bad side effects) and Lexapro (which gave me Tinnitus/permanent ringing in the ears). Is anyone else having this dilemma?  I hate to complain, since I am depression free..and I should be happy as heck no longer being depressed, but I am also very concerned about the weight gain.  Thanks for listening.