Login via SSH onto your VPS.
Run the following:
netstat -antu | grep :80 | grep -v LISTEN | awk '{print $5}' | cut -d: -f1 | sort | uniq -c
It should give you something like the following:
2 105.13.186.116
1 105.229.232.37
1 130.211.226.44
1 165.255.157.202
1 165.255.89.149
78 196.210.20.237
1 196.22.252.129
1 196.220.172.180
1 41.13.124.34
1 41.13.74.50
As you can see the 196.210.20.237 IP is doing a lot of connections to the server.
Try blocking it using CSF or iptables and see if load on your server drops.
