It's not the filter.
I expect it is one of these:
1. pump is bad.
2. the well is running dry. Test for that by turning off the pump for a few hours. See if pressure is a lot higher when you first turn the pump back on.
3. there is a leak in the connection to the pump, which may be down-hole.
4. Something is draining a lot of water up top. Close valves to isolate. (least likely, since you would probably have noticed)
Look for obvious stuff, but expect to call a well company. Ask your neighbors for advice. They will probably know the local reputations.