Heavy, dark, gloppy, kind of stringy period.

A few weeks ago I had an unusually dark, stringy (this is the best term I can use to describe it) heavy period. It lasted a few days longer than usual as well. I've never had one like this before. Then this past week, two weeks after this oddity, I got my period again. This one was somewhat lighter than the last, a lot of brownish discharge with some blood. I'm wondering what could be the cause of this, and if I should possibly speak with my physician.