Maye, it is definitely something YOU are doing wrong. I have over 2,500hrs and have completed 100's of playthroughs in Tactician and Honour Mode, and my main class is the Eldritch Knight.
People thing they need to be Casters and I even saw someone saying that they should use INT as their Attack Modifier instead of STR but INT isn't even the Eldritch Knights Spellcasting modifier so I already know most of you are using the EK completely wrong as it's spellcasting modifier is WIS!
Furthermore, stop using it as a caster. These are FIGHTERS! It is under the Fighter Class for a reason.
Your main priority when building an EK is obviously STR, WIS, then dump everything into CON, it's that simple.
For those of you who are still confused, I'll make it easy for you.
YOU ARE A FIGHTER