No one can tell you how long it will last.
I was a very bright, independent and over-achieving individual before the accident in which I sustained a mTBI too. I worked in a very stressful, male-dominated field: audio for live stage events and tv&film. I had four jobs - one full-time and three regular part-time jobs and additional occasional side gigs. I worked an average of at least 60 hours a week.
After the auto accident I was told I was going to get better within a few hours to a few days. After two weeks I was diagnosed with PCS. Then I was told I'd most likely get better within six weeks. I read that sometimes people just "snap" right back into their normal selves and I was hopeful that would happen to me. Then I was told that most people get "all better" within 3 months.
Six months later I was doing MUCH worse. They discovered a rare physical complication that had occurred as a result of the injury I sustained. They relieved the physical complication and I finally started to get better, but the recovery process has been VERY slow since then.
I wasn't able to work or drive for about a year after the accident I was in. And even then, I could only work 12 hours a week. I increased the hours I work to 20 hours a week in Dec and that schedule still exhausts me.
I want to be all back to normal too. I want to have the same energy I had before the accident. I'm still hopeful that I will. But I don't know when it might happen.
I literally feel mentally disabled compared to the level of cognitive functioning I had before the accident. But I'm still improving so I have hope that I can function better than this again someday.
The accident I was in happened about 19 months ago.
I think experts do believe that most people get better within 3 months. I've read people's posts on this board about people who get better within 8-10 months. And I've read people's posts and PM's on this board about how they've been affected by their injuries for well over ten years.
Those are the facts.
So, try not to worry - experts think worrying and stress make people recovering from PCS worse. (I think if the same experts lost their cognitive functioning and wherewithal they'd be worried SICK.) But, try to stay positive at the same time. I've also read that experts believe that the people who are the most determined and motivated to get better are the ones who ultimately enjoy the best recoveries.