forcast range needs to be changing NOW plus 6 weeks

Hi Guys

If you see the attached document

I am trying to count letters under dates - which iv done with =COUNTIF(D5:AM5,"F")+COUNTIF(D5:AM5,"G")+COUNTIF(D5:AM5,"H")

The issue I have got is the range needs to be NOW preferbly from Monday this week plus 6 weeks in advance.

So the range D5:AM5 next week needs to change to J5:AS and so on. I cant seem to add 7 to column names.

Is there a way round this.

Thanks in advance