Scratching certainly won't help but make things only worse. Put some lotion on them. I had the same thing when I started getting my stretch marks on my pansa and my boobs itched so much that I scratched them so much, then when I finally decided "hey i'll try some lotion" i put some on and you could hear my scream 4 miles away.
This will sound weird and gross, but it should help! Put deodorant under them and in between them, especially if they are really big. And then use some lotion, i use udder butter, on the rest of them. THe deodarant keeps them from getting as sweaty, which helped me with the itching.