Many routers don't have much in terms of monitoring. You can try and narrow down the issue by eliminating factors. Only have your pc online and wired, no wifi connections, and you can use resource monitor to watch if networks spiking to max out your bandwidth. You could probably find some better software with more details. At your router the package iftop is very good for checking current bandwidth and finding the local machine. You can also test your LAN with iperf3. If you have a weak wifi/powerline/anything thats not wired connection you can see packet loss.
It's normal for ping to spike when your up or down is congested. Those consistent spikes could be something like streaming media. It does incremental small downloads unlike a normal download that just maxes until it's done. Finding the source can be a pain without any tools. If you get your ISP to look at it and it's just traffic you're generating yourself they might bill you. All they do is plug the modem into their pc and do a line test.