What Causes Sphere Shaped Vaginal Discharge During Periods?

I'm 17, 5 feet tall, and I'm practically 100 pounds. Medical history... I had surgery for my hand in the past but I'm pretty healthy. I play soccer and I just joined a club. Today, I got my period, but what was strange was that two clear gumball-sized spheres came out with the blood as well. I guess they were soft since they weren't perfectly circular. But I didn't noice them come out because nothing hurt. What are they? I'm not sure of I should be worried or not.