The first thing you need to do to recognize a vaginal discharge as a blood clot or a pregnancy sac is to see if your period is regular. If the current bleeding happens to be within the time frame of menstruation, it should be menstruation. If you are sexually active, not using contraception, and you do not have your period, and after some time you consider that you are pregnant through examination, then the discharge should be watched carefully. You can put the vaginal discharge on the tap water to rinse, if it is a blood clot, you can gradually wash it off. If the discharge is a gestational sac, it can end up being a white cotton ball-like thing, so you can basically be sure that it is a gestational sac. If you are not sure, you can ask your doctor for a laboratory test, which will be more accurate.