External IP Address Issues

Please forgive me if I don't use correct terminology, but here is my problem.

Three days ago my internet speed started getting sluggish. At first I didn't think much of it, but when it persisted I ran speedtest.net. Instead of getting my usual 24+ down and 3+ up, I was getting 5 down and .something up. I noticed here that my IP was not the normal address. I called my ISP about my speeds, they said they didn't know and would send a tech out. I mentioned the new IP and they said it wasn't an issue. I looked up this IP that I was now reporting and the info I got was that it was 400 miles away from me and was a proxy server.

The next day my normal IP was back along with my usual speeds, so I didn't have the tech come out. Now today, I get an e-mail from my ISP saying I have been infected with Alureon malware which is changing my DNS settings and to go to their site and download Nortorn to fix it. I just scanned my system with Sophos and didn't come up with anything. Also, my IP right now is back to this new one with horrible speeds. If I shut down my modem and router for several minutes then turn them on, I first have my normal IP, but it is switched after only a few minutes.

Any advice on what might be going on?

Thank you for your time.