Missed period on the pill. My period!

I've been on the pill for years and have never missed my period before it usually almost comes tues-thurs i got all the symptoms I usually get before my period but no blood (ex. moody, sore breats, bloating) and all the symptoms went away on thurs (ex. no more bloating, no more sore breats, etc) I saw very, very little amounts of spotting but it was too small to tell if it was my period, I am sexually active but don't remember missing a pill this past month I do train MMA and my weight has been shifting up and down frequently the past few months especially last month and I have been stressed but I usually always feel stressed I am going to take an at home pregnancy test today I don't think I'm pregnant but I don't understand why I missed my period