Re: Skim milk??
Sure, lots of moms get told that they must make skim milk. Usually by ignorant grannies or misinformed docs, like yours! This link covers the energy content of human milk: http://kellymom.com/nutrition/milk/change-milkfat.html. Note that what seems to be really important when it comes to affecting a baby's weight gain is the QUANTITY of milk, not the quality.
Your baby has always been a smaller baby, so it's not so surprising that he's still a smaller baby. Seeing a baby's weight percentile drop is normal at around 6 months as the baby becomes increasingly mobile and puts more calories into motion instead of putting them into fat. If your baby seems healthy and happy in other respects, I don't know that I would necessarily be too concerned.
The best thing you can do to get your LO to gain more weight is to nurse more, especially if he is sleeping through the night. You can also concentrate on high-cal solids like avocado, whole-milk yogurt, beans, and meat, and add a drizzle of olive oil to low-cal solids like veggies, fruits, and cereals. A test for anemia may also be a good idea- low iron can sometimes cause slow weight gain and anemia often crops up around 6 months when baby has exhausted his iron stores from birth.
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!"