What Causes Constant Back Pain, Headache, Nausea And Dizziness?

For about 5 months, my 8 year old son has been complaining of low back pain, headaches, nausea, occasional dizziness, has been running a low grade fever. When I thought it was just back pain, he had an MRI of his low back done, which was normal. The pain is getting worse (headaches, back, hurts all over) and wakes him up in the middle of the night. He had a brain CT done last night at the ER, which was normal. He has had a lot of blood work done, which was also normal. He has a brain MRI next week.