It keeps saying my password is invalid but I know it's correct

I know my gmail accout password is being entered correctly but I cannot set up gmail on my new iphone 5 because it keeps saying the password is incorrect. I actually downloaded the gmail app and it works fine from that but not from the iphone mail app. I'm seriously annoyed because I would like both of my accounts to show up in the iphone mail app instead of having to check two separate places. Thoughts?