How do you stay on task with ad/hd?

How do you stay on task? I have severe AD/HD, but have never had meds for it. What are some ways to help me focus? I’ve had a focus issue for a long time, but since I left the Marines it’s worsened quite considerably. I find myself lost in day dreams or off on tangents so much more than I did when I was younger. Should I see a doctor? Or is there a way to keep on task you’ve found helpful? (I’ve recently been turning off the internet to make it easier for me to stay on task, but it just takes a click to turn it back on.) Oh. I’m also over the age of 25 – if that’s relevant.