Is it supposed so hard

I bought Mechwarrior5 few days ago in the sales. Now I played campaign and had difficulty in the 3rd mission. I need to kiil some tanks and planes before destory the base. After that I have to kill a mech. I already have some damages in killing the tanks and planes. It is quite hard, seem impossible, to escape their fire. I have to trade my armor to kill them. Finally the enemy mech destroy my mech. Any tip for noob...thank you.