It depends on the application, however, it is recommended to have at least 1GB of memory for WordPress to serve a small site (that is a t2.micro instance). A t2.nano instance might be enough for very simple sites, with very little traffic or for testing purposes, but it's not enough for most scenarios.
Taking a loot at your results, there is definitely an issue with the memory there, since you almost don't have free memory left.
Did you have a swap file created before? If you don't, you can follow this guide for creating one: https://docs.bitnami.com/installer/faq/linux-faq/#how-to-create-a-swap-file.
If you already had one, you can try to increase it, although we recommend that you scale the instance instead.