You might want to focus more on recovering and eating healthy than on gaining a couple pounds. Unless you're eating like a linebacker, I bet that 5lbs in mostly water weight. You're allowed to walk, no? Take a walk if you need activity. Once you are healed and are active again, you will drop any weight that you might gain during your enforced time off. This is from someone who was sidelined with a broken clav and a broken elbow (different times)--I had the OK to walk during both recoveries and did so. The broken elbow happened when I was 40.