Is the Campy Veloce bb you installed cartridge or cone and cup?
I'd go w/a cartridge unit that is compatible with your cranks.
Pull your bb and reinstall it [ I recommend using teflon or plumbers tape on the cups before you reinstall em ].
Due to your size, make sure that everything is tight: pedals, chainring bolts and the crankarms.
If your problem still persist then I'd consider switching the bb or using a freewheel.