What you are describing is a normal pattern of menstruation and a normal menstrual period. A normal menstrual period last about 5 to 7 days, the bleeding is heaviest during the first couple of days and then slows for the remaining 3 or 4 days. As your bleeding slows, the blood clots. This could be what you are seeing. Another possibility is that you are seeing a portion of the uterine lining (endometrium) which is the tissue that is shed during menstruation. In short, you should be reassured that your period is normal. Because you are of reproductive age, you should make certain that your diet is rich in folic acid and that you are getting enough calcium and iron. You might consider supplementing your diet with these vitamins and minerals.