Hi, My Baby Is 3months Old Fully Breastfed Till Now.

Hi, my baby is 3months old fully breastfed till now. These few days i have notice my milk supply is getting less. I suspect it is due to this hot weather. My baby is crancky maybe getting less milk n her skin also getting dry. I'm thinking to add formula milk to my baby maybe for twice a day. My baby is colicky. Intolerable to cows milk n chocolate. Please advise.