I have a 2 month old son and this also happened to me aboutn28 weeks and then again at 38 weeks. I went to the doctor the next day because it scared me so much but they could find nothing wrong she just chalked in up to body changes during pregnancy!! My son is here today healthy as ever with no complications, so dont worry yourself about it! Everything will be fine!! If you are really worried dont hesitate to see your doctor!!
That may be part of your mucus plug. Don't worry cause I started losing chunks of mine around then, and my baby was a week over due. But I would however inform your OB.