The baby is probably not getting adequate quantity, that is why he is feeling hungry every 20-30 mins.
To increase milk output follow these steps.
1. Try giving night time feeds atleast once
2. Try to feed from one breast , empty it and feed from another breast for the same session.
3. You can try herbal medications like shatavari, it helps in increasing milk output
4. Also avoid bottle feeds wherever possible, it causes nipple confusion in the baby. Try to breastfeed as much as possible.
5. If you wish to give top feeds, you can give katori spoon feeds
6. Improve your nutrition, increase water intake , milk intake, fruits and nuts, green leafy vegetables
7. Try to visit a pediatrician for checking her weight.
8. Continue
vitamin D drops.