The corn has grown! :) Today was weeding on the schedule again and I talked to my boss about my back and feet problems. We decided that I'd just use a weeding tool instead of picking up weed from the ground. After our break we continued and after an hour my back was hurting. I left to find other work, instead of the suggested 'sit down and rest for a while'.
I talked to my boss afterwards and I told her I could weed on the field for an hour at most and then do weeding among the perennials instead, where I could sit down and rest both feet and back. 
My back isn't good at all right now... I did follow a yoga for the back video to try and loosed up a bit and it helped a little. It'll be interesting to see how I feel tomorrow. At least I got the protective things for my feet, so hopefully I'll walk a bit easier.