They initially occurred every few years, but they now happen every few months without any major triggering situational events. There are only two alternative treatments for depression that I have any confidence in. The first is regular aerobic exercise, which can definitely provide a long-term solution. You'll have to do at least 30 minutes of some vigorous aerobic activity at least five times a week, and be prepared to wait several weeks before you see any benefit.
Aerobic exercise is a preventive as well as a treatment.
St. John's Wort is much used in Germany for the treatment of mild to moderate depression, as well as associated disturbed sleep cycles. Take 300 mg, three times a day, of a standardized extract of 0.125 percent of hypericum. Again, be prepared to wait several months before you see the full benefit. Changes in your diet may also make a difference. Try eating less protein and fat, and more starches, fruits, and vegetables.