Blood Clots??(Answers needed)

Whenever I'm on my period, I always get very bad blood clots that cause a lot of pain.
I don't understand why I get them, like what would cause them? 
I don't know anyone else that has them...
I feel like it may be because I have an iron deficiency, or because I skip lots of meals and sometimes don't eat for days and it does something to my body. Does this happen to anyone else? Can anyone give an answer?