S.T.
What's your husband's schedule like? Is it the same?
If that's the case and you have zero quality time for yourself or your relationship with your husband, then you definitely need to change something. But not solely for your son.
First thing I can think of is the job. It sounds like it might be too far away and the commute is knocking you around a bit. I can understand that - I chose earlier hours because of the commute. Is there a possibility that you could change jobs or get into a new career?
No one is pigeon-holed into their 9-5 job. I truly believe that God, in His infinite wisdom, gave you one shot on this Earth for a reason. If you can arrange it, try to work a different schedule out with your job. If not, try to work out some everyday responsibilities with your husband (errands, cooking, cleaning, etc). I'm sure he's as frustrated as you. Put your resume together and send them out this week. Get ready for interviews :) Or check out the local colleges for some training into another line of work.
Your son will fit into any schedule you decide so I'd focus first and foremost on your partner in life and yourself. Without the two of you working a schedule that meets both your needs, your life will become a chore. You don't want your son to pick up on that so something HAS to change. Talk with your husband about what's going on and, remember, men think in logical terms - they don't sit in the "gray" area for more than a few minutes (the "gray" area is defined here as indecision). As an outside observer to your day, you husband can offer some valuable insight on your time management, home management and career choices.
Exercise at work because this seems to be the only time you can get a few minutes to yourself. You'd be surprised at how much you could lose by walking each hour you're at work for only 10 minutes. Take a co-worker with you and, if you smoke, stop. It will help you to lose weight to eat the right foods that are filled with complex carbs to give you a natural energy boost but don't over-do the carbs because you want to have them help you - not pack more weight on.
Steven Covey's tapes and workbooks on time management helped me a lot to understand things in their simplest terms. Perhaps because he's a man and thinks this way but, seriously, it helped to stop the confusion in my own mind and develop a plan of attack for my life, home, career but, most importantly, showing the man I love most in this world that my priorities are clear.