I need less calories now

I went to the Mayo Clinic Website to calculate how many calories my body needs. It came to 1850 calories. This is good information for me because I am trying to lose weight. Some days, I am fine with just a fruit for breakfast and some soup for lunch then some protein and veggies for dinner. Other days I am ravenous and I don’t know why. I think when I awaken early, or too early, like 4:30 or 5 am, it puts off my body clock for the time I need to eat, because I find when i wake up at my normal hour of 7 am, I seem to be fine.