I'm feeling discouraged

I don't know why it's so hard for me to lose weight. I watch my calories and walk for 20 minutes every day.

This is an example of what I've been eating every day for the past year.

Brunch

Smoothie

1/2 cup fat-free milk
5.3 oz sugar-free yogurt: 90 calories
Handful of spinach
Handful of blueberries
Handful of almonds

Dinner

A protein (usually meat)
Vegetable side
Potato, rice, or pasta side

Evening snack

20 pistachios
Stick of cheese