Heat rash on center of breasts

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My second pregnancy and my boobs hAve gotten super large  almost a d size and I'm only 14 weeks. Before I was a small b, but because of the size I've gotten a super bad heat rash and I can't stand it anymore. It's been bad that now it looks like I'm scared. 
Anyone know what can I put so it could feel better and feel more at ease instead of scratching??