Other have answered that this is a standard practice. But, evidently, it was not a standard practice for you, nor you have been notified whether that is the process.
For your own sanity, you deserve an explanation. Don't assume malice, but ask your manager something like:
Hi, I wonder if that's standard practice of peer-review, or you think my work need check?
Also it might be useful to show that you can be proactive and willing to help your manager:
Should I schedule these check myself in the future, so you don't have to waste your time on emails?
This way you'll do few things:
- hopefully get more comfortable, since now you will understand situation and process
- take initiative in your own hands, which is always appreciated
- get clearer picture of expectations. After all, maybe this is a process all new hires go through, and in 4 months you'll be on your own (i assume you are relatively new to the org)
As Joel Spolsky wrote, people are happy when they control their environment. Get more control by clearing this out, not by blindly assuming that this is OK.