I know I'm not eating as much as I should, but I'm never hungry. What's going on?

If you feel lethargic with loss of appetite then it is a medical problem and you should consult a physician but one can live on juices happily for ever if he feels okay. Food, that means solid food is not necessary if you don't feel taste or desire for it and if you have constipation can live on liquids- if you fart enough your system is on and bowels moving- and there won't be any metabolic complications if you won't feel bad psychologically and physically loss of weight below normal.