Missed period...

I have been trying to get pregnant for over a year n half. I’ve been taking Clomid to track my periods better. I’ve been on the pills for about 8 months now, and my period always starts the exact day of when it should. I am about 5 days late, and the past 2 days have had brown spotting. I took a PT, and it said negative. I’ve had tender breasts for about a week. (Not so much today). I’m just curious if brown spotting is something that happens?!? My first pregnancy I didnt find out I was pregnant until I was 12 weeks.