I'm sorry you are going through this. It took me 4 cycles to get in. Its really crushing, and you aren't that non-competitive. its up to you if you want to give it one more go or not. First off, being a doctor isn't the be-all end-all. There are plenty of other great careers. You are sacrificing a lot by existing in this limbo as I am sure you know.
The good news is you added volunteering and a DO letter and it got you an interview.
I think you are going to need to provide some more information. I am sorry if these questions sound blunt. They are not meant to make you feel bad, or regret wasted time. They are questions I asked myself.
1) What schools, exactly, did you apply to? Why so little?
2) You've applied 4 cycles but have 1,000 scribing hours. Working 50 weeks a year at a regular job should be giving you 2,000 hours or so. Are there any other ECs?
3) Did you apply late?
4) Did you recycle your essays each year or write new ones? Who is reading them?
5) Why did it take 4 cycles to finally add volunteering? Were you just a kid with a 506 and 3.43 previously?
6) Did you always apply to mixed MD/DO? At what point did you add DO schools?
7) Did you get interview coaching? Besides getting the scribe job have you ever had an interview before?
8) I bet through the entire cycle you were super nervous, and didn't add any new activities, and when you didn't get in you panicked and sent in another app because why not? Am I right? And as a result you did not change much from year to year.
9) What was your year-to-year list?
My biggest question is: Who was advising you? You should have been told to get more ECs earlier, and apply to more schools sooner, and so on. Are you doing this on your own based off SDN? That is what I did and I definitely missed a lot of things. You really need to apply to like 30+ schools, all the DO schools, anywhere that might look at a low-tier OOS applicant. Your main focus needs to be DO as a subpar MD applicant (unless you actually got an MD interview?)
Anyway, feel free to shoot me a PM if you want to discuss anything in private. You should start looking at a back-up plan at this point, too.