Chondroitin Msm

I am a 46 year old female that is over weight and can't lose any of it.?
Here it is. I had a hysterectomy about 5 years ago and was on Premarin. I had been a smoker for 30 years. I no longer take hormones, I quit smoking in December of 2006. I have gained about 50 lbs. I have for about 2 months changed my diet, I eat 5 small meals of between 250 and 300 calories, low carbs, high protien. I do not drink soda, just water and fat free milk. I have been walking about 3 miles 3x a week and walk about a mile the other days with my dogs. I try to do more exercising but after I walk, my ankles hurt so bad that I can barely walk after a rest. I have changed shoes also to see if that helps. What am I doing wrong so that I can lose the weight? I know less weight would help my ankles. I take a good multi vitamin, Chromium Picolinate and glucosamine chondroitin MSM. Can anyone give me some advice??
I have not lost a single pound. I seem to be gaining.
First, for me 1200 calories a day did the trick. Second, I bought a bike. The walking can be less aerobic than biking, and you use more muscles biking. Next, for me I changed food by eating mainly veggies...a few fruits and less protein. I have lost 15 pounds in the last 4 months...not great but it is slowly getting better. The kicker is I look like I have lost 30 lbs. because I look fit.