Weird Bleeding?

am on the birth control Seasonique which only allows me to have a period every three months and 4 periods a year. I am very good at taking my pills and take them every day and at the same time. My boyfriend and I had without a condom and there was ejaculation on march 15th and again on the 24th. I got paranoid and took two tests about a week ago and both came out lit up negative right away. I was stressing so much that it made me sick to my stomach. I also might have a UTI. About on Sunday I began to have very dark almost black with a tniy bit of blood with clots about medium flow and with small cramps(mostly during the day). It is almost about a week until my "period".What can this mean? Is is just Breakthrough bleeding. I also began a sore throat and a nasty, nasty cold on Monday also. Please Help.