Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
As @stevenzhu mentioned, this 90-day validity period is fixed, and there have been many, many discussions previously on this forum regarding that policy. In fact, the general gist of those is that, if anything were to change, it would be to actually shorten the validity period. Note that there are no plans to do this currently, I’m simply highlighting the notion that short certificate lifespans are a very deliberate aspect of Let’s Encrypt, as they are notably better security practice.
If you would post another topic with some more detail, we’d be happy to help you figure out how to automate the issuance and installation process so that you can just “set it and forget it”, so to speak!
...and like the discussion of non-standard ports, this comes up again, and again, and again. Here's a thread where the subject was extensively discussed: