Are large blood clots normal 6 weeks after having a baby?

I had a baby 6 weeks ago and have now gotten my first period since her birth. I have had golf ball size clots that have me running for the bathroom and leave me with mild pain "down there" after wards. I just want to know if this is normal for the first period after a baby or if it is something that I should call my doctor about. (I had my postnatal checkup at 3 weeks)