Vacuum not picking up much but the hose attachment has no problem

I assume you've checked for blockages and that there's a useful length of bristles on the brush roll. Turn the machine over, and just behind the brush you will see a short length of clear plastic tubing with spiral reinforcing. That tube often splits, so there's an air leak and consequent loss of suction at the brush. A split may not be immediately obvious - to get the tube off, pull it off from the motor end and then unscrew it at the brush end. As a temporary measure you can cover a split with tape, but the tube undergoes so much flexing that tape is rarely effective for very long. A new hose (it's called the internal hose) is not expensive and is the only permanent solution.
If the internal hose is not split, post a reply here and we'll see what else we can think of. Good luck!