I'm always trying to grow my nails out and it always FAILS. I've tried the nasty nail polish to keep you from bitting you nails and eventually I stopped bitting them. I started wearing acrylics and my nails were so thin there healthy now but of course one is always breaking. I use Sally Hansen products and they still break I guess my nails just don't want to grow oh well. But I'm going to keep trying because acrylics are just I'm not sure anyways.
You should try to eat foods with a lot of Calcium and Iodine. Plenty of fish, fresh vegetables especially green ones, kiwi. Foods with biotin. Peanut butter, grains and nuts.