How can I drill through very hard porcelain tile?
Check your Tile bit to see if you have melted the edge. normally it should feel nice and sharp against your finger.  Hopefully you have a nice drill (generally battery operated may be a little on the light side). 

What I do, is get a straw filled with water, or a spray bottle, and get a helper to either "pipette" or spray water onto the hole while you drill. 

Second, keep the drill at slow speed - high torque, pushing hard onto the tile. You should hear it biting into the tile, As soon as you go too fast and see the tile or bit-tip going red, you have probably destroyed the bit (this is especially true for ceramic tiles)

third. as you suggested, some bits actually like it when you move the drill in an orbital fashion. I find that it cuts well on some of my bits.

So basically, if you are keeping the cut surface nice and wet (cool), and you have a sharp bit, you are doing everything right. 

I have previously bought diamond bits like these with very little success. (i think you need to go for name brands here) 



These are the regular tile bits which I speak of. (and I am sure the ones you describe)