So at the end of Watchmen things aren't exactly your fairy-tale ending and I personally found the story kind of inconclusive. Were there any ever comics or books or any material that told the story after the events of Watchmen?
No there weren't.
However, Alan Moore revealed to Wired in 2010 that DC had offered him the rights to Watchmen back, if he would agree to prequel and sequel projects:
“They offered me the rights to Watchmen back, if I would agree to some dopey prequels and sequels.” [...] “So I just told them that if they said that 10 years ago, when I asked them for that, then yeah it might have worked,” he said. “But these days I don’t want Watchmen back. Certainly, I don’t want it back under those kinds of terms.”
The same article also contains a response by DC Comics co-publishers Dan DiDio and Jim:
“Watchmen is the most celebrated graphic novel of all time. Rest assured, DC Comics would only revisit these iconic characters if the creative vision of any proposed new stories matched the quality set by Alan Moore and Dave Gibbons nearly 25 years ago, and our first discussion on any of this would naturally be with the creators themselves.”
In recent years they have published the Before Watchmen comic series, a prequel to Watchmen.
2017's Doomsday Clock takes place in the world of Watchmen, seven years later.
Ozymandias's plot was revealed after Rorschach's journal was published and the world is now on the brink of nuclear war again.
This and 2017's The Button serve to link the Watchmen universe with the current mainstream DC universe.