What Causes Spotting Followed With Cramps And Heavy Bleeding?

Last week Friday April 4th, I started spotting and then I got what I thought was my period it was moderate bleeding but this past Thursday April 10, I started feeling crampy and started bleeding a little heavier now its back to moderate bleeding again. But my breasts are really sore like I am going to get my period but they haven t stopped hurting. Im worried because I dont have a clue about whats going on, I wasnt suppose to start my period until this Sunday. Could I be pregnant?? I feel like I have the symptoms but took a home pregnancy test and came back negative. Or maybe I tested too early?? I could really use some answers, kind of scared right now that something else could be wrong.