Weak back
 

I have a very weak back. I have been to a therapist for it but it is still bothering me. Can anyone suggest what I can do to make it stronger? Any exercises you think will help me out so I do not have to continue to go see my PT?

Weak or injured?

Weak in terms of aesthetics or strength? Why is it weak: injured or lack of training? There's plenty we can do but need some info before we start.

LtL

My PT had me deadlifting milk crates to start with.

Very weak. I was at the PT a few years ago for it, but have not been back in a while. Lately it has been bothering me. I need to start doing some of the exercises she gave me, but want some other advice to help me feel better as well.

go back to the exercises that your PT had you doing, if you are able to.

my suggestions:
light,high rep back exercises that will help to strengthen and as you become stronger add weight/decrease reps.

DB deadlifts, hyperextensions, light GMs, any core work just to name a few!

The only way you are going to get the back stronger is if you do the exercises your PT told you to do. Also walk a lot as this will help your back feel better.