I had two periods, one this month and one last month. i took two pregnancy tests a month after sex. but it looks like a heartbeat in my stomach?

Your own pulse: Slender women can sometimes see their belly pulsating like a heartbeat. It is due to flow of blood in the aorta. Feel your pulse at your wrist. If the two pulses are the same, the belly pulse is your own, not a baby's. (Pregnant women do not observe abdominal pulsations.)

The stomach: is not involved in periods. Timing of periods often vary a bit moreso at starting them (age 13) or ending them (age 50). Certainly with two periods and negative pregnancy tests, pregnancy does not seem at all likely. A thin person often will have a noticeable pulse in the abdomen from normal blood pumping. I am not quite sure how to answer your particular inquiries without an examination in person