A couple of non-professional thoughts...

Something unseen has been stressing your system for several years and in the past few months has overcome your natural abilities to dissipate the stress. This unseen stressor (or combination) may be brain or body chemistry, possibly associated with aging or an untreated medical condition.

You've probably heard about SAD - Seasonal Affective Disorder where people develop depression symptoms during the autumn-winter months. A small percentage of people suffer from Summer SAD. (New York Times: Seasonal Depression Can Accompany Summer Sun, 2002)

Cailin caillte, could you get a full medical check?