I haw a 5 year old boy who used to eat well but for the last few months he is complaining a lot about food. He feels full without eating. Any ideas wh?

Varies. Many children have wide ranges in how much they eat...Even day to day. Your child is complaining about food and has satiety without eating. He needs to be seen by your doctor. Sometimes constipation can do this. Sometimes gastritis (inflammation of the stomach lining) can affect eating. His symptoms merit a visit and further evaluation.
Too much pressure? Well-meaning parents are often concerned that there child is not eating enough and the child begins to feel pressure to eat. Complaints of feeling full or stomach pains at the dinner table may be a sign.