I breast feed. My first gained slowly, always small, because of latching problems at birth. My second is now 3 months, latched immediately, and is robust. My first will be 3 next week. My parenting advice: Don't stress about the weight. The percentages are crap. Parental instinct is HUGE. If you honestly believe that your children are growing up healthy, then they are. (Unless you're a moron, and given that you found this site, I'd say you aren't).
That said, remember that kids need carbs since they're very active. Just be choosy about where they get them. There are a lot of threads about kid snacks on here.
Also, at 3 months, if you're willing, you could get yourself lactating again. Even a little with supplementation is better than nothing. Best shot at preventing disease.
I'm not perfect (or anywhere near) with my paleo eating. My toddler definitely is not. The only soapbox I can stand on is the one about nursing. It gets better as they get older, especially between 6 months to 1 year. Plus, it allows you to eat 500 extra calories of delicious food every day :D
Stepping off the box.
As long as your child is growing, learning, smiling, and pooping, they're fine as far as weight goes. The charts are all a guideline. And when their pediatrician asks what they eat, just say plenty of meat and veggies, and they should be happy with that.