I remember reading a series of books, consisting of a total of three books, maybe 3 years ago (in 2014). The series wasn't very old at that point. The titles contained years.
The scenario was basically our current real world a couple of years in the future - just that there had been a nuclear war, forcing the people of the city that the books were set in underground, where they lived in underground stations.
They could plant mushrooms and either eat the mushrooms themselves or feed them to the pigs to later eat the pigs. There wasn't much other food, as nothing could grow underground without any real light and often without any artificial light, too. The main currency were bullets that could be used to buy stuff or to shoot.
Shooting wasn't necessary most of the time. Only for those who were going to the surface in special hazmat suits, trying to recover some materials from the city above. Those people often died very early because of the radiation or because some mutants got them.
There were quite a few underground stations that were connected to one another. Some of them formed factions. For example the innermost ring was a faction itself and there was a Nazi faction and a communist faction.
The first book starts with the main character in one of the outer stations being sent by a mercenary to a certain station with a message because some unknown mutants were attacking the station and it could be a threat to all of them, which would mean the extinction of humanity. The book focused a lot on social aspects and the daily life he would encounter on the different stations. Throughout the book he has to go to the surface into a library where big mutants await him and there are multiple unknown threats, not just mutants, on his way from station to station. Not to mention the different factions.
I've also played a game that was based on the first book. Sadly it focused a lot more on the "Kill mutants!" part so that instead of rare occasions mutants became the norm and you would kill lots of waves of them. Not quite the feeling I got from the book.
The second book was about a girl who met the mercenary from the first book at is travelling with him from station to station. It was not quite as good as the first one, but the second book was also quite interesting.
The third one is the one I didn't finish. It was written from the first characters perspective again. He was thinking about his actions from the first book the whole time. I would love to finish this series and I can't remember why exactly I didn't finish the book. It was just not as fascinating as the first one.
Could you help me remember what the series was called so I can finish the last book?