Since your baby is preterm he is still learning to take feeds. Usually sucking and swallowing is not very well co ordinated and hence the baby takes a lot of time to take feeds.Give your baby 1-2 weeks more and these things will be resolved. Approximately 30 ml feeds are well enough for the baby at a time, although he may also demand more. If this is the case, offer him as much as possible.
Roughly you should be able to feed him atleast 8 times a day including 1-2 night time feeds.
Next Steps
1. Add HMF sachet in 3-4 feeds in expressed breastmilk
2. Atleast 8 times feeds are recommended
3. Approx 30 ml is good
4. Avoid bottle feeds in between, this causes nipple confusion and hence delay in maturation of sucking and swallowing co-ordination
5. You can also Add 4-5 drops of MCT oil in 4-5 feeds ( alternatively with HMF)
6. Weight monitoring after 2 weeks is recommended