Let me first assure you that this does not mean a rejection. If your paper is rejected, you will definitely receive an email informing you about it. However, having said that, it is a little concerning that the journal hasn't responded to your inquiry. This is a problem with some journals and makes the situation even more difficult for the author.
Since the status changed to "Under review" just 2 days after submission, this is in all probability not peer review; this probably means that your paper is being reviewed internally. Thus, it is likely that your paper is either at the "admin check" or at the "initial screening" stage. This stage should ideally not take more than a few weeks.
I think you should send another inquiry to the journal. Keep following up every week till you get a reply. If you don't get a response even after sending 4-5 emails, you can consider withdrawing your paper.