Little red bumps on chest. (photos)

I acne on my face (which was the main concern) and also a small patch on my chest and back, I have been using Epiduo for a little over a week and I have noticed that only on my chest there appears to be a lot of little red bumps, they don't burn but they itch and I was just wondering if that's normal? and how long would they take to go? As you can see in the provided image the bigger pimples were the ones I began with and all these little one appeared after the week of using Epiduo

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