SqlException (0x80131904): Login failed for user 'DOMAIN\username'

I have created an intranet site that is running fine locally but when running with IIS I am getting a SqlException (0x80131904): Login failed for user 'DOMAIN\username' message. Not sure if it matters or not but I am remotely connecting the server from a different location. I was hesitant to post as I am quite new to programming and feared looking silly but I have searched for days and days looking for a way to fix this. I have checked Windows authentication over and over as well as windows authorization.

Note: When logging in for windows authentication, If I enter the incorrect user details, the window appears again, if user details correct I can access the site. I can then navigate my way around the site until a point required to access the database. Looking forward to a resolution. Currently pulling my hair out.

Can supply code if requried