My weight isn't changing as well as I expected.

I worked really hard on my diet for a while.
At first, I thought I would lose weight quickly if I controlled my diet and exercised consistently, but now that I've lost a certain amount, my weight isn't dropping easily.

I feel a bit exhausted, especially since my weight has stayed pretty much the same for several days even though I’ve been reducing my dinner portions and exercising.
How do you usually overcome a plateau when you hit it during a diet?

Since there hasn't been as much change in my weight as I expected... I think it's hard to stick to a diet.