Is it possible I'm having a Miscarriage?

Gunjan
12 weeks 3 days today and passed  a golf ball size clot yesterday and have been bleeding since then no other symptoms, called my doc and she said to hang in there, I have my appointment on Tuesday she said if you don't get any cramps it's ok to pass a clot as it could be between the uterus and placenta. Not sure what to do?