I got married 2 weeks before my third year started (I'm now an M4). My brand new marriage was difficult through studying and exams and everything else that comes with medical school.
The M3 year takes a lot of work to get through on both sides of a marriage. There were days I'd come home and only be able to crawl into bed. I've fallen asleep in the middle of dinner and struggled to wake up again at 3am. The best way we coped with that year was to understand we were both making sacrifices. My husband would come home and cook dinner for me, wake me up to make sure I had eaten something, though often I immediately fell back asleep. He washed my scrubs and made sure that there was food in the refridgerator because he knew that I would skip meals if it eating wasn't easy and available.
On my side of it, I also struggled to make sure that studying only occurred at school. I got everything done in a few extra minutes now and then at the hospital and the time I had awake and at home was for the two of us together. I didn't volunteer for extra projects and made sure that when he was home, I would be home if at all possible. I may have stayed late post-call at 3 pm, but I didn't go in 1 second early or volunteer for weekend shifts.
On the bright side of the third year, there is the 4th year. I've already finished all of my required courses (with 3 electives left to take) and I have no more overnights or weekends left until I start my internship next year. When I'm home now, I try to be a full time wife, doing the cooking, the cleaning, and spoiling him as much as I can.
My husband really struggled some this last year. He took a paycut to move to a new job (in a new city) so we could be together (we were in a long distance relationship). Then, I never seemed to be home.
We've managed though. Third year is only one year; you are already 1/3rd of the way through it and next year is a big improvement.
One way we coped was by getting a cat. It makes the lonely days a little less lonely.
Everyone is going to struggle with making it through the M3 year, and again when trying to make it through intern year. It'll all shake out though.