Google "knuckling over". I think the information you'll find is on Great Danes-but it applies here as well. The nutrition of your dog isn't sufficient. What are you feeding? You may need to add supplements. Also, try to keep him on softer surfaces-not the cement you have him on in the picture.
4,5 and 6 star foods is what you want: http://www.dogfoodanalysis.com/dog_food_reviews/
I have a feeling you're going to come back with-you can't afford a high quality of food for your dog-since you only get paid once a month...and if that's the case, why do you have a dog? You know there is such things as emergencies right? If there was some big emergency with your dog right now what would you do? Wait until the end of the month?