What Causes Vaginal Spotting With Positive Pregnancy Test?

Okay so I had my period December 8th for about 5 days. I had sexual intercourse the 25 of December And 1of January. I started my early period the 2 of January that lasted only three days. Then five days later spotted a bit then 2 days later spotted again. So I took a pregnancy test and it came out positive. Four days later took one again and it came out negative. And I was bleeding like I guess I started my period again January 24      twice in one month and spotting.