Start of period.

Today is suppose to be day 1 of my period. Yesterday I noticed a little spotting when I wipe. Today I had a bit more ( enough to stain my underwear) I used a tampon but no blood. My question is do anyone else's periods start like this? I'm trying to figure out what is my 1st day so I can calculate my cycle lenght. Otherwise Glow won't help me know when I'm ovulating. Help!!!