lower back pain while cycling

It seems that sometimes when I go long (for me more than two hours) or I "attempt" to stay aero, either in the drops or the clip on aerobars, I get a numbing sensation/pain in my lower back, just above my buttocks, mostly on the right side. I just got a new trek 1000, previously had an older trek 330 steel bike. I did have the bike fitted. I have done longer rides on the steel bike including a century (I did stop at every sag and got off the bike every 15-20 miles with no problems).

I have talked to a couple of roadie friends who said kindly "it is probably your belly pulling your back down and causing the pain, loose the belly" I am 6 foot 1 225 and loosing.

So...do I just need to ride more and loose weight and as I get used to the bike and the fit it will go away ? Or could it be a fitting problem..ie do I need to raise the handlebars/drops..or move the seat more forward ?


I am a newbie, have completed two sprints, one century and some shorter runs (5k,8k,1/2 marathon)....any help would be appreciatted....sorry if this is a stupid ?