You can have bleeding or spotting during the implantation process(when the egg attaches itself to the uterus). This would usually occur around week 3. You might even think you got your period, but the flow will be very, very light and it will be light pink or a brownish color.
You have not indicated the gestational age. Usually, bleeding during first 20 weeks of pregnancy can lead to miscarriage. Most usual period of miscarriage is 8-16 weeks. At the 12th week, there is hormonal take over from corpus luteum to placenta. Sometimes this take over is inadequate and cause bleeding leading to miscarriage. On time hospitalization and hormonal support can save the pregnancy. Your low levels of potassium can be due to vomiting which is one of the sign of pregnancy. Sometimes, stress can reduce the hormonal levels and cause bleeding leading to miscarriage. So, exact cause of your bleeding during pregnancy can be investigated by the doctors. I have given you few reasons, there might be more but your doctor is best to tell you.
