Suggest Treatment For Leg , Foot And Back Pain

My grandaughter who is 5yrs old has been suffering for some time now with leg, foot and back pain which has been getting worse. Over the past few months she has been really unwell and keeps picking up viruses at school very easily. She has a swollen lymph node in her neck which the doctor says is just due to her being unwell. The past couple of weeks she keeps complaining of headaches and stomach ache and being tired. She looks really pale and keeps getting the runs which is just like water and her breath smells really bad. Her bottom and front passage also keeps getting sore she says it insn't itchy but its just very red so not sure if maybe her water might be a bit strong. She isn't eating very much but she is drinking. When she's at school the teacher says she seems to slump towards the afternoon and goes really tired. Could you please give us some advice as to what we should do next. I'm thinking that she should maybe have some blood tests to see whether she has any allergies or food intolerances. She has to go back to see a consultant about the pain in her legs, feet and back but do you think it could all be connected in some way. We're just really worried at the minute.