Ay, I totally get the worry, mama! So from what I've picked up from other mums, diaper rash usually shows up as redness in the creases and folds ng diaper area, while newborn rash (like sa face) tends to be more scattered at random spots, but honestly kung 3 days na ng no diaper at the redness pa rin, it's likely diaper rash talaga, which means yung skin niya is reacting sa moisture or friction kaya kailangan ng stronger protection.
A few of us tried alternating between different barrier creams, Triple Paste and Desitin work well together kasi may different ingredients, and some mums swear by layering: thick layer ng Desitin or Aquaphor, then Vaseline on top para extra protection. The key thing na nakita namin is to pat completely dry (not wipe) with soft cotton pads and warm water before applying, at truly let the air do its work din between changes. One mum friend told me her pediatrician also recommended trying different diaper brands kasi sometimes the material itself irritates, weird pero it happened to her!
Since she's still struggling after three days though, I'd really check in with your pedia or dermatologist para sure kung ito ay diaper rash lang or may infection na, and they can recommend the best cream for your baby's skin specifically. Hang in there!