Aww mama, diaper rash talaga yan, nakakagulat tingnan pero very common sa 5 months old! A few of us tried leaving baby's bum exposed to air as much as possible, changing diapers frequently, at using a good barrier cream like Sudocrem or Bepanthen, pero honestly, if it looks like an actual wound or may signs of infection (sobrang red, may fluid, or fever), you should bring baby to the pedia to make sure it's just regular rash at hindi bacterial or fungal na, kasi iba yung treatment. Malaking difference talaga once the doctor checks it in person, mama.