My heart goes out to you. It's no fun when family aren't as supportive as you want.
My first bit of advice would be to get in contact with your local La Leche League. They were so helpful for me. It's free, you don't have to join but so worth it. The other moms had lots of practical advice. I too suplemented and I was never judged. I wasn't the only one either who suplemented so don't feel like that would be a stumbling block.
Regarding the active child, that can be a lot of fun. ;) Also, as the child gets older, you'll find that you don't feel as "full" as you did when they were teeny. That's normal. Also fussiness is not necessarily a sign of low supply. Check out kellymom.com, it's really good for information. http://www.kellymom.com/newman/04enough_milk.html
As far as your mom saying the milk just goes away... Yes, eventually it does, but not overnight and typically not when the child is still nursing. Just try and relax, ignore mom when she gets on her nerves (as much as you can, right?) and enjoy your little one.