frustrated Mom

Hi, i'm getring frustrated about being a mother. I felt that i'm not doing my best for my newborn son. I have problem latching my baby. I don't know if my baby is getting enough milk supply. My 7 day old son had his follow up check up this morning. His birth weight 2.9kg dropped 2.3kg. My son was also diagnosed with physiological jaundice and is tongue tied. I really don't know what to do. I know i have to be dtrong for my son. I cry a lot every time especially when it's feeding time. Pls help me.