What Causes Spotting, Constipation And Headaches During Periods?

hi doctor,i am 19 year old female, sexually active, 5ft 4 and 8st. i am on the yasmin pill and last week had my 7 day free, i always come on my period on wednesday 11am without fail only this time i didnt come on until bout 4pm wednesday and it was very light tiny brown bit no blood which i never get at the beguinning. it wasnt until bout 10pm that nite that i had any blood but even that was only a little. i usually have a bowel movement bout 5times in the week im on my period but this time i only had 2 bowel movements and am constipated, never am constipated usually. i came off early sunday and even though i ahd bleeding for 3-4days it didnt seem as heavy as what i am usually. also i have had a headache sunday and monday and no matter what i did or took i could not shift it, i have been feeling tired and drained and also needing to pee more ofton than usual. any ideas on what it could be? thanks