This TED Ed video was just released this week - I just love psychology related YouTube's. The video itself is self-explanatory but for an intro, it reveals a better understanding of a word we use so often in our day to day lives - narcissism. This concept and it's related diagnoses are harder and harder to define as we become more and more self-involved via technology. This video, however, presents illuminating details on what it actually is and how symptoms can be so destructive.
No, you're not a narcissist simply if you enjoy documenting your meals on social media. Narcissism, as I always say when identifying any diagnosis, is appropriate to call symptoms that are pervasive and very disruptive to your life. Being overly fixated on social media may be caused by procrastination, avoidance, or self-esteem issues to some degree - all of which can be aided by therapy.