What Causes Severe Leg Pain,frequent Headache And Fatigue?

hello, i have an 8 yr old son who has been complaining of right leg pain; intermittent however increasing in frequency to daily. Not at night & not bilaterrally. He now has difficulty walking; will limp because it aches. This originally started 3 months ago. Xray was done; nothing showed. Also now has been reporting frequent headaches; 2-3/wk; fatigue & decreased appetite. Also as an fyi he has a hx of incontinenta pigmenta. thx