I activated Cloudflare on my blog a few days ago and in their Analytics it shows me that there are 255 pages crawled by Bing, 16 by Yandex and only 1 by Google. Why only one page for Google? Should I worry about it?
You should have a look at this question, Why aren't search engines indexing my content?. Do the respective checks, submit the sitemap, and most important, wait a bit.
Considering your comment, and the fact that it's a blog, we have dynamic content, which Cloudflare doesn't cache and good results from a search engine. Google? Then, the problem is basically about discrepancy in numbers. But that discrepancy is not just between the crawlers/search engines that you mention, it, most probably, is also respect the real amount of indexed content.
You should do a search on all the mentioned search engines using the site: prefix and check how is the situation of your site. If the results of using the prefix are good, then you should use those results to ask on the customer service on Cloudflare about that difference. If the results are not good, then there is a problem on your site that has to be fixed.
If the above results are good, then do not worry about the discrepancy; still is a good idea to ask them what is happening.
" Why only one page for Google?"
We are actually having some issues with analytics. I would be more concerned with what you see in Google Webmaster Tools or Google Analytics than what's showing on our analytics right now.