I weight 150-160lbs and 55. im not pregnant at all or trying to but whenever i lay down, i feel like a pulse in the middle of my stomach if i press onto my stomach gently or i can see my stomach like pulsate without touching, whats that?

You are probably feeling the aortic pulsation ( large artery in the back of the abdomen )

the pulsating you feel when lying down in the middle of your abdomen is probably your abdominal aorta. The aorta is the main artery that comes out of the heart and travels through your chest and into your abdomen . This is normal anatomy and should not cause alarm. A visit to your PCP would be a good idea if you are still concerned and he can get an ultrasound to confirm our diagnosis