Summing a VLOOKUP

Hi There,

I've been trying to add a vlookup formula to my worksheet but so far have been unable to...

What I want it to do is look in the 6 cells to the left and add up points assigned to the letters.

I.e. In H3 I want the total to be displayed. I have added the formula
{=SUM(LOOKUP(B3:G3,{"D","M","P"},{3,2,1}))}

This works fine unless a cell in the range of B3:G3 is left empty, then I get a #N/A error, so I altered the formula to {=SUM(LOOKUP(B3:G3,{"D","M","P","NA"},{3,2,1,0}))}
however, If I have p p p p NA p, rather than it showing 5, i get 7

If anyone can help me out it would be appreciated, hope the above made sense!

Thanks,
Jay