I understand your pain but from a different aspect. When i started this I weighed 195 lbs and I looked pretty healthy. I had always carried a little fat on me which made me look a little bigger than I actually was. When I started eating Primally I lost about 20 lbs over a 2 month period while working out on a more consistent basis. I started to get worried I was getting to skinny but I changed my mentality when I saw how much healthier I was/felt. With this lifestyle most if not all people will lose weight b/c you change your eating habits. You're not eating as many fillers and the food you do eat is what we evolved on so it will make your body run more efficiently. I workout all the time. I rock climb, climb ropes, trees, body weight exercises and sprints. I don't lift too many heavy things b/c of my back but I am started too. This will only help accelerate the process for me as I know it would for you as well.
I was glad to lose the weight b/c I am now going to challenge Mark with a few pics of my own in the next few months. Of course I am also 25 yrs younger than he is but if anyone has proven this will work at nearly any age it would be him. Since I started to think of myself too small I added more high quality fat and almost doubled my protein intake. I've been able to add about 6 lbs of lean muscle and hope to add 5-10 lbs more in the next 3-4 months. You just to to tweak what you eat, the amount and how you exercise. It's not hard to do if you can come up with a good plan and attack it form all angles. I don't count all the fat grams, protein like I should but in your case I would suggest keeping a journal with everything you're eating so you can better track. You'll know if I shoudl add more of this or less of that. I've started ot do this somewhat but still trying to work out a system that suits me.
Today is a new day. You will get out of it just what you put into it. If you have made mistakes, there is always another chance for you. And supposing you have tried and failed again and again, you may have a fresh start any moment you choose, for this thing we call 'Failure' is not the falling down, but the staying down.