Child Having Tiredness, Stomachache, Has Been Pale. Hospitalized. Showing No Signs Of Improvement. Suggestions?

My 5 year old daughter, has been poorly for some weeks now pale, exhausted she bruises easily central tummy pain, loss of weight and loss of appetite , when she does eat she goes extreamlly pale? (off school for 4 weeks) has been in hospital, blood test showed not a great deal though they did a blood film as they were concerned for Luekimia which was negative but did show atypical lymphocytes?? Which they diagnosed viral infection and Gastroenterotis! She is showing no signs of improvement? And I m worried something has been missed as we are now 2 weeks discharged from inpatient. We are going back but thought I could as you for some advice... A worried parent :(