It's definitely run of the mill depression. For me weight loss is one of my depression symptoms. The medication is doing it's job in that department. I'm pretty sure it's the medication causing the weight gain. It is a common side effect of anti depressants. I have been on other ones that do the same thing and know plenty of people who experience this too.
Maybe you could call your doctor and ask if this is normal. Another suggestion would be to get your thyroid checked. I was very depressed, lethargic and I gained a lot of weight and couldn't figure out why. The doc kept trying different anti-depressant meds, but I was still depressed and lethargic. Finally, I asked to get my thyroid checked and low and behold, I have hypothyroidism.
The weight gain stopped and I actually lost weight once the thyroid was stabilized with new med.
Good Luck!
DQ