Hmm, it's tough because 2 things have changed at once. Might be the saddle, or it might be more mileage in warmer weather. It does bear some suspicious resemblance to a heat-rash.

I use chamois cream or butter religiously with no infection problems, and I ride a lot. So I would try some.

Do you have more than one maker's shorts to wear? I get a similar rash from some makers' shorts, seems to be certain materials irritate my skin when I sweat. The more I sweat, the worse it gets. I cannot wear Sugoi or Shebeest for this reason. I seem to have less of a problem in shorts with a higher lycra content. I would also look at the design of your shorts, and the weight of the fabric. The heavier shorts are frequently made with fewer panels, which can bunch in that area when you sit & pedal. Another reason I avoid certain makers, as this bunching area is where I get pools of sweat that turn into a rash.