Well we wanted to find out the sex so it's abit different to your situation. DH refused to discuss names until we had our 19 week scan & knew if we had a son or a daughter. Before this I kept throwing names at him & he just kept telling me to wait!! It was very frustrating so I can sympathise with you.
So on the day of the scan we found out we were having a boy. We decided on his first name the same day, but the middle name took some time. I hated what he chose & now we've come up with something we're both happy with.
Maybe your DH just needs a little more time before he is comfortable talking names. It's different for them as they're on the outside & not experiencing it like we are IYKWIM.
Good luck with naming your baby!!