I Shut My Right Thumb In The Car Door A

I shut my right thumb in the car door a few months ago and I took all the pain I could for a few days then went to the hospital to get treated for it. They told me it would probably fall off, which of course it did. Well the new nail grew in the other ones place but in-between the old one falling off and the new one growing I kept accidentally hitting it on stuff or shutting it in thing's. Now it is this ugly yellow bumpy looking nail. It's splitting and cracking really bad like it's going to brake off again. My question is, is that normal? Also if it does fall off will another one grow in it's place?