Thank you for your query,
As your child is having low grade temperature rise for 3 months, it is better to make a temperature chart of daily recordings and show this chart to your Pediatrician
for better understanding of the temperature pattern of your child.
Any associated symptoms with this temperature? And physical examination is important to look for any lymohnode enlargement and organomegaly
So consult your Pediatrician with the chart and if necessary go for evaluation with basic investigations like CBP,MP,CUE,Thyroid
Hope i have answered your query.