I have a server with Softlayer and before the attack my bandwidth usage/throughput was working at around 0.3Mbps, and then I had an 800Mbps DDoS/DoS attack that lasted 2 days, and ever since my bandwidth usage/throughput has been around 5Mbps to 15Mbps.
I have contacted Softlayer, and they're saying that there is no attack happening. Could the DDoS/Dos attack have caused something to do this?
Yes, May be there is still attack on your server. I think you will have to discuss this issues with your server admin.
Meanwhile, You can check your server process through ps -aufx and top command. And try to check your server connection through following IP. You will get IP and total number of connections with this command.
netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n