Clots

So basically it's my third day of my period and every period on the third day I have a tissue clot. So normally in school we learn that are uterus has lining containing tissue that comes out with the blood. And I have the normal blood clots but this is like a thick piece of tissue lining like you rinse it and it's actually tissue not blood. And I'm wondering if this is normal i mean I've had it for so long and it's literally like a mini birth. I get real bad cramps and then I literally feel it drop and then I push and it comes out. is it normal??????