Please don't take any type of diet pill without talking to your psych medication prescriber. If weight gain on your current mix is a serious concern, that's a necessary talking point with her/him.

It's curious why you only have appetite issues for part of a month. If you are a female, I'd wonder if it is related to hormone changes/PMS. Stuff changes as you get older, and that includes going from mid teens to 20s, not just 30s and older. These issues are a concern for many women, including those who take zero meds.