It's more than likely a fit problem. There are a lot of variables involved. LBP can be because of too long a cockpit or too short for example. How are you riding the P2K, at what seat angle? The best thing would be to see a pro bike fitter with tri experience. As this is limited in your area you could post a few photos here for analysis if you have a digital camera. The isn't the best solution but it might help pick up any obvious fit problems.

Another factor could be the time of the season. I went out for my first ride of the season last week when the weather was nice and before we got slammed with an out of season snow storm. I had left the bike in my end of season ride position from last fall as I rode my other bike on the indoor trainer in winter. When I got back my low back just killed. It's too early in the season to ride like that right now since I have to get my body back into shape and flexibility.

Mike

I had a similar problem when I first got my P2k (before I discovered this site and read the numerous threads on Bike fit)- I think that lower back pain is probably a "fit" issue.

The p2k allows you to have the seat post in two positions - which way round do you have your seat post ?

I collected my P2k set up with the seat post in the "normal" looking position and my lower back killed me (having been pretty excited about my new toy - I was a little (very) disappointed) - however after reading the discussions on this site I reversed it and I was much more comfortable - my weight was taken on my elbows rather than by my lower back. I can now cycle +70 miles with no back pain.

Rgds

Pete