Yup, it is also called a secondary viral infection. Minor but irritating. My kids have the sensitive skin too. Love that Aquaphor! Oatmeal baths can help too. This can be done in a couple of ways. Aveno makes these packets to put in your bath water ( they look like instant -to eat - oatmeal). Or you can use a blender / food processor to turn some regular cooking oats to a fine powder that you can then put in the bath water. And last but not least , take whole oats and put about a cup in the toe of an old stocking and swish that around in the bath while running the water. It can also be used to "scrub" the skin. Of course the tub will need a good scrub too , rinse the tub right away, you know how hard it is to remove dried oatmeal;) My oldest got the chicken pox when he was little --before the vaccine was common--he loved the oatmeal bath.
And as kinda gross at it sounds don't give him head-to-toe-with-soap bath as often till his skin clears. These can be really hard on sensitive skin. Do wash hands and face often of course.
Keep on with what you are doing and follow your Momtuition. Hey, my youngest is 17 mos now too. :)