lighter period than normal, could i be pregnant

For some reference, I never have regular periods. My last period began 2/21/2010 and ended around the 26th. During the month of march, i had unprotectd sex twice, once on the 4th, and the other a little later than that. My period for the month of march, started late, on march 28. Having irregular periods is normal for me. But i noticed that the first day, it was light, more pink than red, with some ruddy brown. then the next day, it was heavy for a time, deep in color, like a normal period, with some like goopy, tissuey, jelly like spots. Since that day, my flow has been fairly light, and i typically bleed more heavily with my period than i am now. Its been 4 days, and im still bleeeding, althoug its light. Im worried i may be pregnant. but i have no symptoms, really. The only symptom i have is slight breast tenderness, which often accompanies my period, and i also have a history of fibrocystic breast changes, and have had a cyst before in my right breast. so pain in the area is nothing unusual. Other than that, business as usual.Is there a chance that im pregnant, or does it seem more unlikely. Just scared to take a test right away.