how long has it been happening before balancing? maybe rims wasn't put back on properly. Do you have aftermarket rims? check if the centre hub is the right size, otherwise the rim won't be truely centered, and 5 studs won't be strong enough to keep it centred after driving for some time. it only takes just a few 0.xx mm off the centre to cause vibration. It happened to me when upgrading my stock rims to aftermarket, need to go back to the rim shop to get some centering hubs.
or perhaps the rotors need machining? with my old rotors that fixed the vibration for quite a while (until I swap to 17" rims - then it became the rims' problem).