Oo, parang diaper rash yan base sa description mo, lalo na kung concentrated sa diaper area! Best thing is to check with your pedia to rule out other stuff like heat rash or fungal infection, kasi ang treatment varies talaga depende kung ano exact cause, a few of us moms learned this the hard way, hehe.
In the meantime, try keeping the area super dry, change diapers frequently, and maybe skip the plastic pants for a bit para ma-breathe ang skin niya. Sending good vibes, mama!