Can lack of seratonan cause one to always feel tired?

Possibly: Although there is no perfect way to test this theory, many studies have shown a relationship to depression and seratonin. Most medications used to treat depression revolve around seratonin levels. Because one of the hallmark findings of depression is fatigue...The answer to your question is that this is a possibility.

Not most common: Tiredness alone would not be a common way that lack of serotonin would present . Serotonin is considered our feel good hormone. It is part of the melatonin pathway however and a lack can lead to difficulty sleeping and subsequent tiredness , or could be part of a depression-but would also expect mood symptoms