I know how you feel and it ***** :( im currentl . 4 months pregnant and my depression just keeps getting worse especially with stuff going on around me :(
I used to be one of those people that believed that depression was "just a mind thing", but then realizing I was fighting demons of my own, pretty much, my entire life and didn't really fully realize it until I had a nervous breakdown recently and ended up in the psych ward at the local hospital (voluntarily). Now, people being over-medicated for some diseases of the mind is another story, though. :)
As far as taking medications "for the rest of your life", it's hard to say. It depends on what is causing your depression, how you're able to handle the depression and how your body "adjusts" to the medication. You might find that after a few months of being on the medications that the doctor may try taking you off them slowly to see if you have adjusted mentally. But, if there are "triggers" in your life that might be causing the depression, you may continue to be depressed until those triggers are removed.
However, if you are still feeling down even though you are on the medications (Pristiq is more for bipolar disorder, I believe), then you may want to switch to another medication. I was on Effexor which made me manic, then I tried Wellbutrin which made me more depressed and finally wound up with Prozac which seems to be working pretty well, except for the sexual side effects, but those are common with any SSRI and SNRI.
Different people react differently to different medications, so it's hard to say how things will work out for you.
It can take a while for medication dosages and mixtures to get to a level they really help. Pristiq may not be the right antidepressant for you or it may simply not be at the therapeutic dosage for you just yet. You need to make an appointment with your psychiatrist to discuss what you are experiencing as some adjustment seems very necessary.
As the above stated, it's hard to say whether you will need the medication for the rest of your life. You may or you may not. To stand a better chance of making it without meds in the future, I would definitely find a therapist you feel you can be open and comfortable with to begin discovering causes, triggers, and symptoms as well as tools to help combat the symptoms.