Having trouble with the nutritional balancing act

I have lost 123 pounds so far, but have about 50 more to go. I'm having a hard time balancing the calories, carbs and sodium. I have high blood pressure and have to limit my intake to 1,500mg a day. One example is cheese—it's low-carb but very high in sodium. When I find low-sodium options, they're high in calories and/or carbs. Just when I think I have something figured out, I get the notification that I'm eating too few calories. I have no problem at all with lunch or dinner, but the snacks are killing me. Fruit is so high in carbs, but many of the other options are equally as high in sugar, sodium, or both. I'm at my wits end and trying not to go into starvation mode to get my weight loss moving. I just had both knees replaced and am beginning to do some exercising, which I couldn't do before. I just need some help figuring out what kind of snacks won't break one of the rules. Any suggestions appreciated.