Spotting before period?

I have never experienced spotting before until approximately 3 months ago. I started spotting the week before my actual period and it last about a week. Im on the pill but i did take a pregnancy test just for peace of mind. It was negative. The following month there was no spotting and i had my normal period when expected. This month, I'm expecting my period in about 4 or 5 days. Yesterday, I began spotting again and it has continued all day today. My boyfriend and i do not use condoms as i have been on the pill since age 14. What could be possible causes? I recently turned 25; could it just be my body going through some change? Should I be worried? Asking for some help/advice/peace of mind. Thank you!