I usually recommend feeding at least every 2 to 2.5 hours (measured from start to start) during the day and at least every 3-4 hours at night if a baby is having difficulty gaining weight. I would also usually recommend pumping after each feeding to increase supply and offering breast milk as the supplement rather than formula.
If you aren’t making enough milk it’s b/c the baby wasn’t latched well initially. If the latch is ok now you should be able to make enough milk. The reason the latch is so important is not just for your comfort, it’s also so the baby get extract enough milk. When the baby is latched more toward the tip of the nipple it inhibits the flow of milk. When the baby is latched well the milk flows more readily and usually babies suck better too. Since the amount of milk you make is determined by how much is taken out of the breasts, getting a good latch is important for milk supply.
If your baby is fussy I’d offer the breast. Don’t forget to allow your baby to cluster feed b/c that’s when the baby will get more of the higher fat hind milk.
Here’s more about feeding routines and cluster feeding:
What's a normal breastfeeding routine?
http://parenting.ivillage.com/baby/bbreastfeed/0,,8n69dpmw,00.html
If the feedings are short it may be b/c the baby isn’t fully awake. Here’s more on encouraging better feedings:
Sometimes feedings are short b/c the baby isn’t fully awake. I usually strip the baby to his diaper and t-shirt then do some baby ‘sit-ups’ gently rocking the baby back and forth while I tickle the ribs and up and down the spine. If I think I have the baby awake, I’ll pause, do nothing and watch the baby. If he remains awake and starts to try to suck his fingers or makes some noise then I know I have the baby fully awake and it’s ok to pass him off to mom to bf. If the baby goes back to sleep as soon as I stop tickling him then I need to work on getting him more fully awake before handing him to mom to breastfeed.
Once the baby is on the breast he should suck deeply and rhythmically. If he pauses longer than about 5-10 seconds you can get him started sucking again with a breast compression. Hold your breast in your hand, very close to the chest wall, with four fingers on one side and the thumb on the other side. Firmly squeeze the breast pushing it toward the baby without sliding your fingers down. Hold for 10-30 seconds or so and then release. OR, you can try to get the baby sucking again by stroking under the chin toward the neck with moderate pressure. If you do a compression and/or a chin nudgie a few times and the baby doesn’t start to suck again, or only sucks a few little sucks, then you can take the baby off the breast.
If the baby comes off the breast before 10 minutes I might try to wake him again and put him back on the same breast. If you try to wake him, only try for no longer than 10 minutes. If the baby isn’t waking in that time try a bit later.
Here are some more links to help:
How do I know my baby is latched correctly?
http://parenting.ivillage.com/baby/bbreastfeed/0,,9jw927vm,00.html?ice=iv|hy|pp
Is my baby getting enough milk?
http://parenting.ivillage.com/baby/bbreastfeed/0,,8rr83zjm,00.html
And once your baby is gaining weight well for at least 2 weight checks I usually recommend weaning off the supplements as described here:
Weaning from supplements:
http://parenting.ivillage.com/baby/bbreastfeed/0,,9w8tjqsd,00.html
Keep us posted on your progress.