Welcome! By tracking your food, using the food log, you can see how many calories you currently eat. Then make an attempt to increase that number yourself with food choices that are higher in fat (which is higher in calories per gram than protein or carbohydrate). Gradually increase the frequency of your meals. These are just some suggestions.
But for inflammation in your wrist, the best help will come from your doctor. For that matter, you can ask him about gaining weight while you're in his office. I'd be surprised if he didn't tell you just to increase your caloric intake with more healthy foods.