Baby is already a low birth weight baby. I believe breastfeeding is not established yet so I think mother needs help related to that. Child needs adequate feeds so that weight gain is appropriate and rising trend should start after 7 to maximum 14 days. Take help for establishing breastfeeding and urine frequency should be 6+ in 24 hours atleast and also weight gain should be 150 to 200gm per week So follow up with your doctor every week for now. Otherwise child will start to have several problems.