Newborn keeps on lifting up his legs

Hi I just give birth to my newborn 2 weeks ago. Wondering if it’s normal for my newborn to lift up his legs while lying down? Any idea what’s the cause of it? Is it because he pass motion after feeding? Anyway, i breastfeed him and sometimes, i will give him formula milk. #1stimemom #firstbaby #BreastfeedingJourney