Is it possible at 5weeks pregnant to feel a ball-like object in your tummy when lying down on your stomach?

Not the uterus : At 5 weeks, the uterus is only slightly enlarged & you should not be able to feel the top edge until 12 weeks. Unless you have uterine masses (fibroids), multiples, or some other growth; your pregnancy should not be the reason. See your OB & have them check what you're feeling, it could be a small hernia, bowel distension, or a lipoma. Take care.