Let's see what we can do to help!
Are you using the stock Email app? Can you try logging in to your email account whilst using an internet browser? Have you tried logging into your email on a PC or laptop to see if the same issue persists?
We'd also recommend trying the following:
> Soft Reset: To do this hold the Power button and the Volume-down button for a few seconds until your phone restarts.
> Clear the cache and data, follow this link here to see how it's done!
Hope this helps!