Our hunger is affected by many, many factors. Some physical and some emotional and some social, etc.
Also, sometimes our hunger just goes in cycles. "Normal" eating is sometimes being hungry and sometimes not being hungry. The theory is that your body will eventually sort itself out. If your body really really needed food (and you weren't suffering some sort of illness that would prohibit feelings of true hunger and/or medicines that make one lose your appetite or something) it would tell you. It would make
you hungry. On its own.
That being said, there are many many ways of easily getting in nutritious high calorie foods if you don't feel like eating much. Sooo many foods are calorie dense. Just eat a bowl of granola breakfast ceral instead of low calorie cereal. Eat a few ounces of nuts for a snack. Drink a smoothie with full fat or low fat (not nonfat) milk/yogurt and higher calorie fruits like cherries or bananas and maybe add in a couple tablespoons of regular peanut butter. Eat a bagel. And the list goes on.
That also being said, if you are still concerned please do go see your doctor! S/he will be able to assess your
situation in a much more informed way.