Aww, common yan sa babies especially pag mainit at maraming sweat! Try keeping the neck area dry talaga, wipe it gently after feeds or if nakita mo siyang nagsweating, and make sure loose ang damit so air can circulate doon. If it's not improving in a few days or lumalaki na ang redness at may signs ng infection, better check with your pedia para sure what's causing it at makakuha ng proper treatment!