Why do you even think you are getting DDoS attacked?
I have worked on a lot of peoples websites and forums who thought they were getting DDoS attacked and it was never the case. In almost every situation at least that I have dealt with, it was simply bots hitting your website and causing server overloads.
I had this happen on my forums about a year ago maybe and I used
Ban Spiders by User Agent along with a few htacces goodies and some ip range blocks to stop bots from terrorizing my forums.
This is more likely what you have and not a DDoS attack. If you were actually getting DDoS attacked and if you are on a shared server, your host would quickly look into it and do something about it because it not only affects your website but a whole lot others as well.
If you want I can take a look for you if that is the case, I would of course need an admin account and access to your cPanel to monitor what is going on throughout the day. Send me a private message if you still need help.