When I combine this post with your other one about having a 12 yo son who has become a difficult tween, I understand more about the possible reasons that cause you to be are tired.
Dealing with the pre-teen and teen issues is difficult both emotionally and physically. One of the reasons that we become so overloaded emotionally is that being involved with their attempts to become independent brings up our own unresolved feelings from when we were that age. I was in therapy with my daughter when she was that age going thru those behaviors. My therapist suggested that having this happen could be a good thing for me because it enabled me to process my feelings from that age. Turned out to be true.
My 9 yo granddaughter is acting like a tween in many ways. I've been pleased to find that so far I've not had any strong feelings about her hit and miss rebellion. I know I'm able to stay calm and be more consistent because I am a grandmother and not with her all of the time and don't feel as responsible for her behavior. At the same time, I see my daughter sometimes reacting in an angry and inconsistent way with her daughter, just as I did with her. Maturation is an ongoing process. Unfortunately, parents often have much work to do right along with their children. Thank god for grandparents who've successfully negotiated parenthood!? To my daughter it doesn't always seem like a good thing.
You have a new stress with your son's taking the next step towards adult hood. He doesn't have the advantage of viewing his actions from the far side but you do. Hopefully, you reached adulthood without too much pain and reached it being able to be a responsible adult. If so, your son will also succeed just as you have.
If you had much pain and had to learn responsibility the hard way, it's possible that he will also have difficulty. If you are aware or can become aware of how his behavior is a process of learning and that you can allow him to make mistakes while teaching him how to behave to prevent the big, life altering mistakes that some teens make you will have less stress and a more successful relationship.
I'll stop here and go to your other post for more suggestions on that subject.
As to being always tired, exercise will help! The older we get the more important nearly daily active physical exercise becomes. I think that our bodies start breaking down while we're still in our twenties. I began to feel it in my late 30's and really feel it in my 50's. Without exercise we become tired and even physically weaker.
I get my exercise by briskly walking. I look at my watch. When I'm 15 minutes out I turn around and walk back. I try to walk anytime the distance and timing is such that I can. I park in the far reaches of the parking lot. I take the stairs instead of the elevator.
I need more muscle strengthening exercise now that both of my grandchildren are getting too big to pick up. Before, I somewhat equated picking them up with lifting weights. lol
I took a 40 minute low impact aerobics class in which we used weights and want to get back to doing that. In the meantime, I'm lifting food cans above my head when I take them out of or put them in the cupboard. Looks silly! But I can feel a difference.
On the advice of my doctor, during my annual physical exam, I started taking Vit. D, a new scientific discovery that helps us stay healthier. And after my 70+ yo friend's doctor suggested she start taking a Vit B complex pill, I started that. I've been taking a probiotic combination pill for awhile. After I'd been on the combination of supplements and pills for a couple of weeks I've been less tired.
Over my lifetime, I've learned that depression also decreases my energy. Having a 12 yo son can make one depressed without our realizing it. The degree of depression can be related to our possible buried and left over feelings from our tween and teen years. That may be something that you want to consider and deal with.
Otherwise just the stress of our sense of responsibility for and need to deal with our children's behavior and feelings can cause us to be tired.
It is actual tiredness and not "just in our head" as some would like us to believe.
It's been my experience that being sure to have a healthy diet, taking supplements, exercising, finding a way to recognize and deal with our own feelings, as well as finding ways to be successful with parenting and other life issues will increase out energy level and allow us to feel happier. Being tired is a complex issue. Once illness has been ruled out it's up to us to figure out how to help ourselves. You've asked a really good question! I wish you success!
The vit D is what we get from the sunlight. New research has found that some of us are not getting enough Vit D even tho we may get out in the sun. In the Pacific NW where I live there may not be enough sun for us to get enough Vit. D. lol