Aww mama, ang dami nang babies na may ganyan sa first month, heat rash, prickly heat, or sometimes just normal newborn skin adjusting pa lang siya. One of my mom friends' baby had the same thing at cleared up na after a few weeks when we made sure na dry lang siya always at hindi sobrang init, pero kung concerned ka talaga o parang lumalaki lang, better check with your pedia para ma-rule out kung may underlying cause, they'll know agad kapag nakita nila. How's baby doing otherwise, sleeping and feeding well pa rin ba?