I'd say 2b, especially if that was taken this time of year. The way that it looked after you'd let it out of the bun was actually the tip-off as far as I'm concerned, my hair tends to similarly self-straighten in a bun.
Dark brown BSL 2B - when I was a baby, strangers would ask my mom, "Did you perm your daughter's hair?"

For the record, that isn't me in my av! Camera crapped out, and so have to make do with pics of twins