Your pregnancy hormones are the culprit - especially the changes during the first trimester. I read this on WebMD, "The higher level increases the skin's production of natural oils. It's hard to predict who will develop pregnancy acne. You have a higher risk, though, if you have a history of acne or have acne flares at the start of your menstrual cycle. If you do not develop acne during the first trimester, it's unlikely you'll have breakouts that are out of the ordinary during the second or third trimesters."
Hope this helps.
Lala Ling