Wheeeeell ... I hate to laundry list you but there's a whole list of things it could be.
- What version of Raspbian? (cat /etc/os-release)
- What kernel version? (uname -a)
- What does timedatectl tell you?
- If you ping 8.8.8.8, what do you get? (you will have to hit ctrl-c to get it to stop)
- What does it show when you issue the command: systemctl status systemd-timesyncd.service
If you just want to set it and walk away for a while, issue the command
sudo timedatectl set-time '2019-04-03 14:30' <- (Single-quotes required, change date/time appropriately)
If you are running Stretch,
someone in their infinite wisdom decided ntpd worked too well so they screwed it up and swapped it out with timesyncd.
Depending on what the above tells you, there's different ways to remedy the issue properly.