From your update, it sounds like some of the tips have already helped a little bit. And in your original post, it seemed like you already know what you need to do...it is just a matter of finding the motivation to do it. You've already gotten some great responses here, and I'm probably repeating a lot, but just wanted to add my two cents.
You mention being in a junk food rut, and not wanting to eat that, but needing the sugar for energy...it really is a vicious cycle. If you try cutting out that sugar, you will probably find that you are more energized. Plus, sugar is addictive, so it is hard to cut it out, but once you do, it becomes easier to eat those things that are better for you. Others have already mentioned some great snack alternatives. Some of my favorites are homemade granola, homemade granola bars, popcorn, cheese and crackers, hummus and veggies, plain Greek yogurt with maple syrup and frozen fruit or granola, mixed nuts, fruit and yogurt smoothies. Also, I always feel more energized when I start the day with eggs or oatmeal. Something with protein to keep you full and energized. I have also found that eating more whole grains has helped me feel better overall...I still eat processed breads and pasta occasionally, but I try to eat more oatmeal, rice, quinoa, whole grain breads, etc., and I have so much more energy and I feel better mentally and emotionally, too. Another good addition to any meal is beans...super economical, energizing, filling, and tasty. I also simply don't buy junk food...if it's not there I won't eat it, and I'll save money and my health. If I buy junk food, I inevitably eat an entire bag or box of something in one sitting...not very economical or healthy.
I also second the responses to get a little exercise. Even if you don't go to the gym, just taking a short walk every day or doing some gentle stretches or easy exercises you can do from home are helpful. It might sound kind of silly, but if you have a clear space and an empty wall try a handstand. Being inverted really energizes you. Handstands are great to strengthen your arms and core and to help with balance, but they really do clear your mind, too. Instant energy boost.
Also, some things that have already been mentioned, but that I really like: drink lots of water, reflect on the things you're thankful for, try to cut back on internet/tv time, take a minute or two to meditate (simply deepen your breathing for a few minutes a day...this is especially helpful for those times when feeling irritable).
And don't worry about trying to change everything at once. Try a few things at a time. See what works for you. And make sure you are doing things for yourself...it is good to take care of your family, but you can only take care of others if you take care of yourself first.
Finding that motivation is the hardest part, but I think that can only come from you. There is no secret formula or magic tool to find motivation. You have to just want to make a change. I think if you set an intention each morning to try to be positive, it will be easier to find that motivation.