If the leaves are curling up and drying from the bottom up you may have curly top virus which is transmitted by beet leaf hopper bugs. I've had this problem for the last couple of years and it's very discouraging, my Black Prince tomato has over 60 tomatoes on it but it's dying so I'm going to have to pull it up. The only way I know of the prevent this is to keep them covered with row covers so that's what I'm going to do this fall when I plant more. Others may have more information and this may not be what you've got, hope it recovers and produces for you.