In a Nutshell
Yes, your ISP and government can read your emails, even when using encryption because of a number of vulnerabilities, and the fact that most emails are not encrypted on email provider's servers.
Definitely Not in a Nutshell
Your ISP can employ a number of tactics to read encrypted email: firstly email does not use HTTPS, instead it uses the SMTP protocol which can use StartTLS for encryption, I say can, because many times StartTLS is not used. This is because STARTTLS is opportunistic, so it will encrypt when you, your email provider, and your recipient meet certain criteria. This makes it fairly easy for your communications to become insecure by forcing certain conditions that disable StartTLS.
This is why many emails are not encrypted in transit. Although, some email providers are good about this, like Google, so Gmail to Gmail communication is encrypted in transit by default, many others are not.
But for the purpose of discussion let's say that all your emails are encrypted, and that your ISP isn't doing anything that is making them travel in clear text, even then your emails can be read if the government wants to read them because nearly all emails are not encrypted end-to-end. Meaning that even if they are traveling encrypted they are not encrypted on the servers of your email provider.
So if your government really wants to know what emails you are sending, with a search warrant, they can know. The mantra of the security/privacy community has been that emails are consistently insecure, even when using encryption.
What You Can Do / Extras
With a fair amount of work you could make your emails secure, but that requires the recipient of your email to cooperate, a luxury you may not have. I recommend avoiding email if you are concerned about your privacy, and if email is an absolute necessity I would recommend reading about STARTTLS, PGP, and this post on stackexchange if you are interested.
- K-9 Mail ( Open Source Email Client With End-To-End PGP Encryption )
- Mailvelope ( For Encrypting Emails through web mail )
- Cryptocat ( Encrypted Private Chats in your Browser )
(Sorry, I can only post two links on here )