If you are eating a nutrient rich diet, with plenty of fresh fruit, veg, protein - meat, fish and pulses then you are producing a complete milk for your baby. You should not need to supplement with anything. If you are vegan then there may be a b12 deff riskbifvyou know you are defficient.
Keep up the good work breast feeding and if your baby is content and gaining weight, don't worry about supplements.
I was told at one of the weigh ins at well baby clinic - I used to go every week and then every two weeks until they were 6 months old as very low birthweight babies- they told me when we chatted about weaning.