Backwashing and pump pressure

[TRDaniel]

I have a 16 x 36 in ground pool, using sand filter with baquacil chemicals.
My pool needs backwashing about every 2-3 days due to lost pressre at the returns. After backwashing pressure/all is good for a day or two? water is usually clear and perfect chemically. Just pressure lost?
please note the following:
1) I have changed the sand annually, this is new sand
2) I do not have a pressure gauge on my pump, do I need one?
3) This is a new problem, last summer and the start of this pool season only, is there different spec's on sand, could I have the wrong sand?