A:  At the point where you've tried what is inexpensive and less taxing and it has failed--when you've taken the pills, consulted friends, distracted yourself with B movies (which I often recommend!), patted the dog, went to the gym more often--and you still can't feel better or figure out why you're suffering, then that's when you need a professional. 

Why a professional (i.e., someone trained in the process of psychotherapy)?  Because at the point where your familiar coping strategies have failed, you are facing ongoing overwhelm (whether it's obvious to everyone, or more subtle and interior), and folks without experience in working with this situation can actually make things worse, even though they have the best intentions.

A professional therapist knows this terrain, and when to propose challenges, and when to offer support, in the service of decreasing the overwhelm and increasing the hope and motivation.  When we're lost, we often will benefit with a good guide, who has traversed the gullies and crevasses, and knows the safest route from A-B, from stuckness to motion, from despair to hope.  A therapist doesn't provide magic, but just (ideally) good guidance.

Now, that said, your own process of deciding that you're at this point of "Help!", that may take a day of insight, or 20 years of trying different strategies, or for some, banging your head against the problem.  It's very individual, but when everything else fails (relatively few go to therapy without a crisis in hand), there's the recognition that you need something more, and that's where therapists live.