Anti Depressants

The main thing to understand is that the weight gain isn't a direct side effect itself. There's no mechanism by which the meds will cause you to store fat without excess calories.

What is likely happening and certainly sounds to be the case, is that the medication isn't helping with the depression, quite possibly worsening it, this, as you say reduces motivation and desire to do anything. So you are moving very little and potentially had an appetite increase with the meds too. Those two things very easily cause people to gain weight on lots of different medications. I've been through it myself.

So number one is to speak to your doctor about not having an alleviation in symptoms/worsening and see what your options are. That should be your main focus right now.

Number two is, if you can, put your details in here, pick a low goal, maybe half to a pound a week and do what you can to stay within that goal, no need to be perfect, just try to get into the habit and see what an appropriate number of calories looks like for you.

But to reiterate, see your doctor as a first priority and discuss dosage or change of meds. Do not come off them yourself, you have to be very careful, side effects coming off need to carefully managed.

Disclaimer: I am a psychiatrist and this is not medical advice. It is general information about depression and the treatment of depression. Any treatment decisions should be made jointly between you and your doctor, not people (even psychiatrists) on the interwebz.

One of the symptoms of depression is lack of motivation, so you may need a different antidepressant. However, talk to your doctor about this and the concerns about weight gain; there are some antidepressants that don't cause any weight gain, some that cause weight gain in people who are sensitive to them, and some that cause weight gain in almost everyone who takes them. Sertraline is one of the ones that causes some to gain and not others.

Also, it is absolutely not true that you shouldn't be on an antidepressant for longer than 6 months at a time. It is generally recommended that for a first episode of depression, 9 months to one year is the time after which you can try, with your doctor's oversight, to taper off them. For people who have had more than two episodes, it is extremely likely that they will have more if they do not continue on the medication indefinitely.

That said, psychotherapy is also a really good option for treatment of depression, and may be just as effective as medication for mild to moderate depression. If you have access to a good therapist, please take advantage! They can help you not only get over a depression but also learn the warning signs and the strategies you can use to prevent future episodes, whether you end up needing medication or not.