Why is it I'm hungry for certain foods at different times?

Cravings and hunger are not the same thing.

Sweet and pasta are similar as they both have a lot of carbs, but I guess mostly you are referring to the salty vs. sweet. If you drink a lot of sweet drinks like coca-cola, orange juice, punch, then you probably don’t crave sweets much. If you have not eaten anything in a long time nor consumed much sugar during the day, the body might look for a fast sugar fix like sweets. Salt is extremely important to keep fairly constant in the body, so the body is pretty good at craving salt to keep the level at where you typically consume throughout the day. If you don’t eat the usual salt intake, your body has to start flushing out water.

Also, a lot of it is habit. If you usually eat certain foods at certain times of the day, you will probably crave those things.

Because then the world would be boring. Craving the same scientifically engineered health cube 3 times a day like a pill would be very dull.

Because the song is actually true; Sometimes you feel like a nut. Sometimes you don’t.

Are you pregnant? lol

“There is no single explanation for food cravings, and explanations range from low serotonin levels affecting the brain centers for appetite to production of endorphins as a result of consuming fats and carbohydrates.

Foods with high levels of sugar glucose, such as chocolate, are more frequently craved than foods with lower sugar glucose, such as broccoli because when glucose interacts with opioid system in the brain an addictive triggering effect occurs.

The consumer of the glucose feels the urge to consume more glucose, much like an alcoholic, because the brain has become conditioned to release “happy hormones” every time glucose is present.

The craving of non-food items as food is called pica.” Source.

In addition to what @gailcalled said, I think that hormone fluctuations can play into cravings as well. And also simply needing certain nurtrients that might be in those particular foods.