Do not worry its the lining of your ovaries. I too get it at times. All you can do is to keep yourself clean by changing your pads or tampoons at regular intervals.
Abnormal periods are cause enough to go to a gynecologist. There are several causes to this, like hormonal imbalances and things like polycystic ovary syndrome.
The blood clots are probably not something that would cause too much concern, but I'd bring it up with your doctor either way. That said, be aware that in your period, you're not only shedding blood, but also the endometrium, which isn't so much the lining of your ovaries as it is the lining of your uterus. So perhaps not all those "blood clots" are exactly clots, but could be bits of other tissue. Still... bring it up with your doctor of choice. I would really suggest visiting the doctor soon, as bleeding that frequently likely isn't normal.