Spotting before a due period; could i be pregant?

My period is usually always on time, if not just a couple of days prior or late to the due date. my cycle is about 35 days per most periods. usually i wouldnt be so worried if it was a few days late, but this time, i discovered i was spotting a light brown discharge and im sure my period should be due soon, hopefully in a couple of days. i always have protected sex with my boyfriend and we are always careful. i mean ALWAYS, but could there still be a chance of pregnancy? i took a pregnancy test last night (30 days since last period) and it came out negative. i should be relieved, but i'm not convinced because i have never had spotting and reading the forums on this website has scared me even more.

please advice. much appreciated. =)