First off, I'm sorry for what you're going through. I'm not sure why a Dr told you to take a pregnancy test because those can come up positive for weeks after a miscarriage. What you should have done is gone for a repeat bloodwork to see if your hCG hormone is rising or falling. In a healthy pregnancy, it should double every 48-72 hours.
As for passing a large clot and still being pregnant, yes it is possible. I had what is called a subchorionic hemorrhage where the sac seperates from the uterus causing bleeding and I passed a very large clot. But, my baby was unharmed.
I strongly suggest you go to your GP and get 2 hCG blood draws 48 hours apart. That should tell you if the pregnancy is viable. Again, I'm sorry you have to go through this. If you have any other questions, feel free to inbox me.
Thanks. OB told me yesterday to stop Utrogestan and see her today. Still lightly bleeding, took another preg test this morning and it showed same result. You're right, i will request for another bloodwork whenI see my doctor later.