I've also always worked from home, the past 15 years, except for a brief 3-year stint running an office about 8 years ago. Working from home means lots of time indoors, and not usually much excuse to go out and about. You don't need to leave the house to get to work, which means you don't have to leave work to get home either. You may not have to head out for lunch, although you probably should.
I find the things that really helped me the most:
1. Buy a seasonal affective disorder lamp, to ensure you get enough serotonin release to keep mood high and banish lethargy. Not mumbo jumbo, very important.
2. Do something you love with a passion, not something to simply make money, otherwise you're wasting your life and probably sabotaging your own potential. Have you considered that you might be miserable because you're ONLY trying to make money, it's not easy, and you don't enjoy it? This has all sorts of negative consequences for health, state of mind, etc. If you love something, you get good at it, and then there is always a way to make money out of it.
3. Helping other people makes you happy. So try to find a way to help others often. Work in a local charity shop one day a week. You'll meet customers and you'll be thanked a lot for helping out

You'll feel good about yourself
4. Go for a walk every so often.
5. Avoid coffee, eat well. Time spent indoors without sunlight will cause lethargy and the last thing you need is to top it off with insulin spikes and crashes.
6. Be productive = avoid self loathing
