I had my period for less than a day and then nothing?

around june 14 or 15th i had some light spotting / old blood or whatever, but i didn't think too much of it, because i've read that that's normal before or after your period. on the 20th i woke up at went to the restroom around 10:30am and there was nothing, but when i went to the restroom again before work around 11:45, my period had started, and it was all normal. but the entire day at work, i had absolutely no more flow... and it's been like that since then! so a little less than two days now. my periods can generally be irregular in timing sometimes, i think because i'm underweight and probably get stressed a lot, too, but they're never weird once they've started like this. they're always 7 days, with the first three being the most steady and heaviest. basically i'm just wondering if anyone has any idea what could be causing this weirdness, and if it counts as my period starting or what. thanks!