What Causes Spotting?

My period is usually irregular and I just started to get dark brown discharge yesterday. I assumed it was my period but was worried because it was very light and I didn't have to change my pad. Today, I still have brown discharge (a little more than yesterday as well as some red blood).. but the problem is more of what looks like my 'period' seems to come out when I urinate or wipe, as opposed to on my pad. Should I be worried?