What I can tell you is that renting a DDoS attack is both cheap and very easy.
My guess is that an unexperienced user (or maybe a couple of them) are renting these services for 1 or 2 hours and repeating at different times of the day. Sustaining an attack for 24h/7 might cost more than the person is willing to pay and may also be irrelevant, i.e. you just need to affect the site during the peak hours.
If my guess is correct, it is pointless trying to find out who is doing this. You would need to contact these "companies" providing such services and ask who is paying them to attack you; repeat for every other such company.
The only reason I'm posting this is that I missed it in this thread, so I'm not sure if people are aware of how easy it is to launch a DDoS attack.