N.S.
The best advise I can give you right now is not to make any life altering decisions when you are in the midst of a storm. So, don't figure out now whether you should leave your marriage or not. Try to sort out what is reality and what is caused by pain meds. It sounds like you are under A LOT of stress. Stress can cause headaches/tension headaches. There might be some other meds you can take for the headaches. There are also wonderful exercises that you can do to aid your body deal with the stress better.
I would strongly recommend that you find a medical doctor that will work with a counselor/psychologist/psychiatrist in finding the right treatment for you.
Also, it would be good if you and your husband can start somewhere in your relationship that you are not arguing about and start to enjoy each other again. Maybe you like to go for walks together, or watch movies together, etc. Just something that will start to build your marriage and not tear it down. Is there anyone that can watch your 5 year old for an hour or two every week that you can use to just be together with your husband as a couple?
Please remember that you and your husband are in this together. He is not your enemy and you are not his. You got married b/c you love each other and you had hope for the future. I believe that the two of you can learn to strengthen each other in the journey you are taking together. Finding a new and/or better way to communicate is always important. Please don't rush into a decision. Find out how you can get your physical pain under control and then deal with the emotional and mental pain. Maybe you think that your son won't see you as much seeing how much time away you spend from home anyway, but believe me, in the long run, your son will benefit more from you and your hubby trying everything in your power to work things out and make it better, than from you walking away. If you and your husband can find ways to bicker and fight, then you can find ways to build each other up. It's a hard and long road but one worth to walk on. You will come out much happier and full-filled in the end and you will be an inspiration to other married couples that are struggling.