Hi, it's completely normal to feel fatigue after lifting weights. This is due to your muscle fibers breaking down, which requires time to repair, which is how muscles grow. Although, if you still feel fatigue more than a day after your workout, your workout may have been too intense and straining on your body.
It’s normal to feel a bit tired after exercising, especially if you’ve pushed yourself a bit! I find that if I’m tired and hungry, I tend to get irritated much more easily.
By “diet is good” what exactly do you mean? Are you eating a good variety of foods, with all the necessary nutrients etc.? Are you eating enough? Do you eat something before you lift, and something after which includes both protein and carbohydrates? Are you consistent, do you eat throughout the day? Are you properly hydrated?