I have read various accounts from survivors of concentration camps, Japanese POW camps, and Russian Gulags. You lose sexual urges after being starved and overworked so that you are constantly hungry and constantly tired. All you care about is food and sleep. Remember, these people slept with rats, bedbugs, cockroaches, and often were infected with sickness. In one account from a Gulag, the suffers watched a black sheet of bed bugs move across the walls over the beds and victims. Add to that the constant smell of human sweat, puss from infections, diarrhea, and vomit. Every morning you had to remove the bodies of people that died during the night. Those sort of conditions would dissolve any sort of sexual urges.

Also there were documented prostitutes for camp workers. Mauthausen is at least one example and there is a small memorial to the prostitiutes there even today.

I don't believe OP intended this to include camps like the ones Japanese-Americans were put in, but I'm curious how birth rates, fertility and sex in general were in those.