I feel that way; I am a single mom with a hyperactive 7 year old boy. I drive by the gym every day and wish I had time to go in, or for that matter, even the energy to consider it. I set my alarm every morning for 4:50 to wake up and start doing crunches or something in the living room. (That snooze button needs to be replaced with my son crying or something- no mom can sleep through that...)
At this point, I have never actually pulled myself out of bed that early to start doing crunches, I cannot bring myself to go to bed before 11, and I'm not motivated enough to start walking or jogging on my lunch breaks at work. After work is out of the question, it takes all my energy to watch my son, get dinner on the table, and do my daily chores. What my point is is that you are not alone, all moms go through that. With three kids I can't relate completely, but I know what it is like to want to work out but having time nor energy to even get around to by the end of the day.
What I have found that could work in a positive way is taking vitamins and supplements. I started taking B-12 vitamins a couple of weeks ago with my normal supplements and it has upped my energy a lot. Water is also another huge underestimated energy source. My own research has pulled up the organic apple cider vinegar and honey remedy for energy, weight loss (and appetite suppressant). Finding time to work out means less sleep in my book as getting up extremely early in the morning is the only option that seems feasible. The extra energy is the only motivation to work out that I can think of other than having a giant mirror in the hallways that shows you at every angle in the morning.