If you have been depressed before and had a recovery, then you can do it again. Maybe accepting that it is happening will help keep the period short as well, because that horribly difficult acceptance part always has to come first. But you don't have to feel that you have not done enough or failed in someway. Depression is an illness, and one that tends to reoccur in people who have already had it, so perhaps stop seeing yourself as to blame in someway. I would just focus on getting better from where you are, however annoying it is to find yourself here again, that is where you are right now. But you already know the way out.
When I used sertraline I found it to be really helpful on a low dose, 50mg a day was like getting a good night's sleep for me and helped me out of two depressive periods in the past.