Anyone else passing this kind of clot?

I am 16 years old but ever since I had my period at 12, I have been passing these weird large V-shaped clots on my period on the third day each time. It is unlike a regular clot and is also firm. Every time the thing passes on the third day of my period, I experience really bad cramps until it comes out. I try to talk to my girlfriends about it but they do not experience the same thing. My doctor also told me it is nothing serious. Is something wrong with me or is this normal?