Try moving the moveable ballast forward. It has an effect of moving the pivot point of the boat forward, placing more sail behind the pivot point to help power the bow through the eye of the wind.

Thanks, consider it done.

There's not enough information here for a diagnosis.  The amount of wind and current, and your VMG, would be a good start.  

The boat needs to have some flow across the rudder in order to turn at all, and needs to be going a couple of knots in order to swing the bow through the eye of the wind.  It may just be that you're going too slow into the tack and the rudder is stalling out.  

If you're going to windward you need the jib.  The difference between the handling with the jib set and with the jib stowed is striking---in light air AND in heavy air.

Watch the video here at about 1:30.  That's in very light air---the water is almost glassy, but she spins on her heels.  The boat would still move under main alone in those conditions, but slowly enough that the rudder might stall.

The first thing to try is sailing with the jib.  Please do not move the ballast.  It won't make a difference in handling in any case, and the boat should always be trimmed level fore and aft.