From my understanding of neuroscience low motivation has nothing to do with Serotonin and the Prozac probably won't do crap to resolve your low motivation. I also suffer from low motivation, Dopamine is the chemical your brain is low on when you are low in motivation. Dopamine regulates the motivation to act, study shows

Here's a video about dopamine, motivation and confidence. The Dr. even gives you non-pharmaceutical ways to increase your dopamine. if that doesn't work you could always ask the doctor for a MAO inhibitor.

Prozac has a tendency to "poop out" due to increased tolerance and stop working and even make your depression harder to treat in the future by wearing out your serotonin receptor. Prozac is also full of fluoride which destroys your pineal gland, the hormone gland in the center of your brain that creates your serotonin and melatonin (for sleep) naturally.