So, there's this plant…

… growing in my flower bed, and I have no idea what it is! 

Several weeks ago, I was weeding and watering my raised flower bed (in which I have planted vincas, lavendar,basil, blue sage, begonias, dianthus, and moss rose) when I noticed a few strange plants coming up. I began to pull them, thinking they were weeds, until I noticed one that had grown large enough to put on small, white flowers. I had intended to put a bell pepper plant in this garden, and actually let one with a full-grown pepper die in the flower bed before planting it. I thought these plants were perhaps little bell pepper plants coming up, especially when the white flowers started putting on small, round, green things. I have let the plants continue to grow, and several others have sprung up throughout the flower bed. Now the green thingy’s are turning a purple-ish/black-ish color. I have confirmed that it is not a bell pepper plant because bell pepper flowers have 6 petals; my mystery plant’s flowers have 5 petals.

Does anyone have any idea what this is? I have searched high and low online, and have turned up nothing to give me a clue.

I have taken a picture of this plant and can post it on my blog if that would be helpful.

Puzzled,

Lindsey