It's hard to answer this, but if you need to know for sure, you can see your doctor. Depending on how far along you were, blood tests will be able to help answer the question.
This article - https://www.webmd.com/infertility-and-reproduction/understanding-miscarriage-symptoms - describes what you may see is "a blood-clot-like material, or a gush of clear or pink fluid that passes from the vagina". It sounds like it may be what you are describing, but obviously, I didn't see it, and I'm not a doctor to know for sure.
You may never know for sure.
Have you been diagnosed with endometriosis? Here are some articles on it - https://www.webmd.com/women/endometriosis/default.htm Blood clots are for sure a possibility with (or without) endometriosis.
Hi there. Was wondering what ended up happening? Mind giving an update?