Physiologically speaking, short and frequent feeds are better for milk supply boosting (hormone surges and keeping breasts emptied frequently) and getting enough milk to baby. You don't necessarily feel "full" when it's time to feed. As livingsky said, by the time I feel full, it's been too long (like 4 hours the other night).
Not gaining for a week and still being below birthweight at 2 weeks out are flags for more investigation. You were using nipple shield, right? Were you pumping in conjunction with that? Shields are rather notorious in connection w/supply issues because they don't allow for the same mechanism of milk transfer as a deep latch without shields. Are you still using a shield? Forgive me for not reading back through--I think you mentioned this a while back.
I'd say you should spend a day or two in bed w/baby, skin to skin as much as possible. Offer a feed whenever baby is not deeply asleep, even at the littlest wiggles, or at least every 2 hours, setting an alarm if needed for nighttime, allowing for a 3-4 hour stretch of sleep at night. Do breast compressions with sucking bursts to boost intake and thus, your supply. Take a look at Jack Newman's website for great videos (good drinking vs. nibbling, breast compressions, etc). Consider adding a few pumping sessions between feeds to boost supply, and you can feed the expressed milk with a spoon or cup to "top off" a nursing session and boost intake and weight gain. Consider an IBCLC visit.
Keep a log of feeds and wet/poopy diaper counts for a day or two. Should be at least 6 wet and 2-3 seedy yellow poops (US quarter sized) in a 24 hour period.
Hope any of that is helpful, and good luck!