What Causes Early Heavy Periods?

I had a normal period on Dec 19, my periods on average are 34 days long...I believe I ovulation on Jan 6th I had some pain on my ovaries. My period in not due until Jan 23rd but this week I bled on the 11th a little bit then slightly heavier on the 12th...it was on and off bleeding. we have been trying to conceive for a while now and I had severe pms symptoms since the day of believed ovulation..I took a pregnancy test the day before the bleeding began. Is it possible i'm pregnant still or was that an early period? typically my periods last 4-5 days