Will I know when it starts working?

I did my first shot of 8 units on Monday night so I know it's very early, but I'm not sure exactly what I'm supposed to be feeling. I fortunately haven't had any side effects, but I don't know if I feel anything at all? I think I've been eating smaller portions, but I still woke up craving an Italian hoagie for breakfast.

Will it be like a switch is flipped when it really starts working, or is it a gradual build?