Let’s Encrypt certificates only have a duration of 90 days.
What you need to do, depends on how you got the certificate. If you plan to manually issue certificates using some kind of a tool/website and then upload them to Bluehost cPanel, then yes, you’d need to renew them by hand that often.
Usually Let’s Encrypt is meant to be used in an automated way - e.g. Bluehost integrates it and it automatically renews for you. However this isn’t always the case because hosts don’t always support free/automatic SSL, so you’re stuck doing things manually 
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If you can link your domain or what cPanel server you are hosted on, I can check if it has AutoSSL enabled (a cPanel feature for free automatic SSL).
Also, here’s a big thread of hosting providers that integrate Let’s Encrypt, but Bluehost isn’t there.