I had been riding happily for about 8 years , then last year I bought a WSD TREK. I became such an uhappy rider that I actually thought I might have to give up riding. I had horrible back pain and foot numbness. The discomfort would start as soon as I started climbing then last throughout the ride.

My professional background is in healthcare, so I knew that the numbness was probably from nerve impingement not a bloodflow issue. The back pain seemed to come from the angle of the pedal stroke.

I finally sold the darn thing. Thankfully the problems went away as soon as I got a different bike.

You may want to have a professional fitting done on your bike, but this didn't help me (twice). Changing stem length and saddle position are possible options. I wish you the best of luck in solving your problems, if all else fails rent or borrow a bike with different geometry to see if you get relief.