Hello and I hope I can help you today. Any woman having unprotected sex is at risk for pregnancy, however, You do not have to worry about being pregnant right now because the HCG test is extremely reliable if performed correctly in diagnosing pregnancy. The most common sign of pregnancy is a missed period. If your period is coming regularly every month, it is extremely unlikely that you are pregnant. Feeling your pulse on your abdomen is not unusual when you are thin, you are just feeling the beating of your abdominal aorta, which is the large artery connecting your heart to your legs. So in your situation right now. you can rely on the results of the pregnancy (HCG) test and feel confident you are not pregnant. I hope I was able to answer your question and that this information was reassuring. Best wishes, Dr. Brown