There is the abdominal aorta that runs through there. If you are thin and lay down, some people can even see their pulse there. I don't think that your doctor doesn't give a big F but rather this is actually something we all have. It's disconcerting and fools a lot of people. A lot of women aren't aware of it and think it is their babies heart beat when they start paying attention to that area. You are not the first person fooled by it! https://healthfully.com/can-feel-heartbeat-stomach-5673198.html
Hello~I have had it, and I know the more I worry about it or think about it, the more I will feel it. It is normal as the abdominal aorta runs through that area and it of course has a beat. I would try not to worry, perhaps if you forget about it, you won't notice it as much.