Is my weight gain because of my antidepressant meds? Sleep meds? Age? 20% gain in one year!?

I take antidepressant med for major depression. It's Cymbalta 90 mg each day. I also use prescription sleep aids for chronic insomnia, and hormone replacement therapy for night sweats and other symptoms of my age. I'm a 49 yr old female, had a hysterectomy several years ago, leaving me with one ovary still. I have had a 20% weight gain in the last year. What's going on?? Could it be the meds? Is it my age? What's all the hype about "metabolism"? Oh, I also had my colon removed 4 years ago because it stopped working. My ileum was reconnected to my rectum, so I don't have to wear a bag. I just have to be near a toilet within 1 hour of eating. Thanks for any advice!