My pre term (7th month) baby s weight at birth was 1.940 and at time of discharge on 18.05 it was 2.35 and on 23.05 weight was 2.75. since last 3 to 4 days I have taken him off formula feed(number of feeds decreased to 4 to 5 feeds in place of 12 feeds) and taken him on breastfeeding. His weight today was 2.880. should we be worried?

No worries baby is gaining weight slowly and steadily generally babies dont gain their weight during first month but your was pre mature he is gaining good weight keep breastfeeding

It's always good to exclusively breastfeed.. the weight will increase gradually.. don't worry..
Sharing a few articles to increase Breastmilk I'd required..

Remedies To Boost Breastmilk Supply

Ways To Increase Breastmilk Naturally

Dont worry, the special rcp to increase breast milk is drinking plenty of water, drink 4 to 5 litres a day. Also you can make daliya porridge with milk, it helps.