I've often felt on the edge, but I describe it as constantly treading water and trying to keep my head up. It's exhausting. Never invalidate your feelings. I think you're worried about the label that 'being depressed' would feel like. We all go through varying degrees of depression and no one can rate that but you.

I would encourage at minimum a depression daily journal, where you rate your depression from 5 (felt good, competent) to 1 (felt bad, totally on edge). Sometimes my ratings can change during the day too, depending on life events. Those tidbits might be helpful to discuss with your T and may reveal some thought patterns going on that could be worked on through Cognitive Behavioral Therapy (CBT).

Good luck