Dynamic Form And Memory Limit?

I've built a function that open a form in Design mode, read records from a table about appointments and create a grid with textboxes representing one appointment each. On the left there are labels with hours and as column headers there are doctors names. Practically each column shows each doctor's daily appointments (it is a medical clinique).

Every time i change the date all controls are deleted and rebuilt.

But after three or four day I pass I get a message of memory limit.

The question is general : Why the memory finish if I close every variable I use during the creation with the instruction:

set frm = nothing
set newTxt = nothing
rst.close
set rst = nothing