I have missed my period almost 3 weeks now and it always comes it is suppose to

I have missed my period almost 3 weeks now and it always comes it is suppose to...I have a 28 day cycle ... i thought my period came when i saw some brownish stuff on the underwear... but my period hasnt come.. Once i saw a lil blood on underwear but i didnt pay it any mind..my breast are getting heavier and more tender by the dayright now they are not touchable.... I am more frequently constipated than normal and is very confused.. Are those signs of pregnancy?  is there a chance am pregnant?