Re: Weak Suck, pumping and bottle feeding :(
Excellent advice from the PPs. I would immediately disregard your doctor's advice about decreasing feeding frequency- it is recommended that even bottle fed babies be fed on demand, and not on a schedule! Also, fast weight gain in the newborn period is normal for breastfed babies: some will gain a pound a week in the early weeks. Weight gain generally levels off around the middle of the first year as baby becomes more mobile and starts devoting his calories to action instead of packing them on as fat.
Meanwhile, let's get that baby on the breast as much as possible! I would talk to your LCs about 2 things: first, renting a professional scale for home use, and two, finding a way to feed baby at the breast all the time, even if supplements are necessary. I recommend the scale because you can use it to figure out exactly how much your baby eats at the breast, simply by weighing the baby before and after nursing and subtracting the before from the after. If your LO is eating around 2 oz every couple of hours on average, then you can just nurse him and not bother with bottles and pumping! If he isn't, then you know there's still an issue- maybe with the tongue-tie? Or simply with flow confusion?
Since it sounds like your baby is predominantly bottle-fed at this point, I would really like to see you try an at-the-breast supplementing method like a Lact-Aid or Supplemental Nursing System. These allow you to give supplements at the breast rather than by bottle, and while they can be tricky to finesse they also mean your baby learns that all good things come from the breast, and they can help you to transition to exclusive nursing.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"