In infants the most accurate way to know whether your baby has fever is by measuring the rectal temperature. The normal temperature for a baby should be within 97F. It is crosses more than 99.5F then you will find the forehead, back or stomach hotter. The immediate remedy in such cases is to provide OTC paracetamol or ibuprofen like Nurofen.
if it is just above 99 to 101 then just breast feed the baby the temparature will reduce if it is too high just consult a doctor