I always found smiling to be a forced affair for me.
I do it; and at this point in my life I can project feelings through the strange contortions of the facial muscles, the eyes, etc.
But it’s usually rather odd to me. I tend towards a plain face. No expression. I fight it because it’s been culturally imbued into me, but my nature is generally somber. I fake it well for the cognitive benefit of others; people expect smiling and they’re happier if i do it. I also exaggerate for entertainment. But by myself? Just a regular face.
I don’t see the old pictures as unhappy at all. I see them as neutral faces.
For example, a few months ago, I relaxed all of my facial muscles and took a picture. That’s my neutral position face. I don’t consciously allow my facial muscles to go neutral like; again, cultural training – but if I’m working or relaxed, I suspect I look like this.