Talk to Gynecologist on Breastfeeding

Hi. I gave birth to twin girls 3 weeks back. They were born at 36 weeks and were kept in incubator for a day where they were fed formula milk with cup n spoon. The paediatrician suggested I breastfeed them alternately.so I used to feed one twin myself and formula with cup n spoon to other.twin 1 didn't latch for 5 days and I was quite depressed about it but then she started to latch but won't drink much.in the meantime I got frustrated from feeding with spoon n switched to bottle.now I was pumping,breastfeeding n bottle feeding both twins.now the problem is I want to go back to breastfeeding and bottlefeeding and even though twin 1 latches and sucks there's hardly any milk coming. Twin 2 is latching but she starts to pull nipple really hard and now my nipples are really sore and hurt a loI don't have cracked nipples as yet. Plz advice me how to increase breast milk.im getting hardly half ounce from both breasts if I pump