His weight is on the 25th percentile and his height is between the 90-95th percentile which indicates he is normal for his age. At 3months it is recommended to only start with infant rice cereal (mixed with breast milk). Juices are not recommended until 6-8 months old and orange juice not until a year old to prevent allergy to citrus. Infant Cereal (1-2 Tbsp) 2 feedings a day. Stay with breast feeding as his main source of nutrition.
If your son is 3 months old then i would not give him fruit juices. His stomch will not be able to cope with the acids, etc in the juice. Stick to breast milk for now as this is his main source of food. If you want to start introducing solids, try baby rice to start with.