So, pregnancy can occur any time a penis without a condom is inside your vagina. If you haven't done that, pregnancy is not a concern. So then you have to look at why you have irregular bleeding. It happens sometimes just out of the blue. If you are a teen, it's even more common to have occasional or often irregular bleeding. Somehow you seem to be having another period. I'd have said you were having spotting but it sounds heavier and with clots indicating shedding of your uterine lining. Just start to track it and if this continues to happen, you should talk to your doctor about it. You may need the pill to regulate you. good luck