Clots?

Okay so I'm 16 and I recently went to the doctor because I had an iron defencency which was affecting my period and I got put on birth control. I've been on it for about a month and I have noticed that I've had clots and I've never really had them before. These clots aren't little either (I know this is probably tmi) but they're probably a little bit smaller than an oarnge. I just don't know what could be causing it and if I should be worried. Any ideas of what it could be?