First of all, if you've been doing the same amount of work at the gym for a long time, it's no longer helping you to lose weight but is helping you to maintain your weight where it is. At your age, though, it's going to be hard to increase what you're doing -- you're working out pretty hard for your age and your level of natural fitness might not allow you to do more without getting injured. I know; I'm a 64 year old man, and have always done a lot of exercise, and about your age I started getting hurt from it. So don't go nuts about exercise. But you might try changing up your routine if you've doing the same thing for a long time. See if more cardio helps. Then see if more resistance work helps. Change it up, and see if it gets that metabolism revved up a little more. If you can work out harder without hurting yourself, try it -- even just 15 minutes more each time will help. On the other hand, I'm never sure what is meant by pre-diabetic. For some people, it means there's a family history. For others, it means your blood sugar is testing at border-line high levels. If it is, then your diet isn't as good as you describe for you -- it might be great for someone else, but isn't working well for you. Without knowing everything you eat daily nobody can tell if it's as good as you think it is, but even it's great and it's not working, it might mean your particular digestive system just isn't doing well on what you're eating. I don't know. You're not that overweight, and if you're muscular you might have more weight than when you weren't. I know I got heavier when I started weight lifting. You might also look into whether you're taking any medications -- many of them make you gain weight no matter how much you exercise and how well you eat. There are all kinds of hidden sugars in foods as well you might not be counting. But bread isn't the problem -- white flour is a problems, but the least obese people around the globe are grain eaters. There are other factors involved. You might have heard of the famed "Mediterranean Diet," which isn't actually one diet but a series of different diets eaten in that part of the world. These people eat a lot of bread and pasta and grains in other forms, so those who say grains are the source of weight gain just aren't looking at real people. It's much more complicated than that. So what can you do besides varying your exercise to make it work again? Vary your eating habits, and see if something works. One example is eating small meals through the day instead of three meals. Maybe it helps, maybe it doesn't. Make sure your thyroid and pancreas are working the way they should. Eat foods that help metabolism such as hot herbs such as cinnamon and turmeric (cinnamon in particular helps with blood sugar as well, as does certain adaptogens such as American ginseng and holy basil). Try eating less meat and more bean protein meals. Know that only moving while you're at the gym doesn't compensate for being sedentary the rest of the day, if that's your habit. It helps, but not completely. Try eating fermented veggies such as kim chi that can help your digestive system. What I'm saying is, if what you're doing isn't working, try something else especially if what you're doing is pretty good, as what you're doing is.
I know someone who recently went through a similar challenge and once they eliminated dairy, poultry , pork and red meat from their diet they lost 5pounds in 2weeks. I think there's something to eating more veggies, some seafood occasionally , healthy grains(like quinoa, brown rice), peas and beans and no chicken , turkey , pork, red meat. I don't advocate all or nothing but try it for a month and watch your intake of added sugar products like ketchup and pasta sauces.