Hey Kathy,
It's definitely inactivity. I've put on about 10 lbs over the last 3 months. I've been trying to watch what I eat (I eat very healthy, but I've been eating a lot of meals as studying makes me hungry--the brain needs all that glucose).
I wouldn't sweat the weight gain in the short term. However, I know it is really frustrating. Keep healing and when you get more active, your weight will start to normalize.
I will admit that I have an inner "fat kid." I used to play football in high school and I was my biggest my junior year -- 210 lbs at 17 years old. I dropped down to 142 when I started college at 18. I started lifting weights and bulked up to 180 lean and ripped. I stopped lifting again in 4/08 and I've dropped about 25 lbs of muscle and I'm right around 180-185 now...so all that muscle is gone and my body fat % has gone up even though my BMI is normal for my 6 foot frame.
Bad thing for me is that if I eat unhealthy for a week, I can put on 10 lbs of unhealthy weight. Good times...
Good luck Kathy...I know it's frustrating.