If it gets slower and slower, I guess it have to be that you are creating more and more records. But it could also have something to do with your FileMaker Server.
Is your FileMaker Server a dedicated server, meaning there is no other software installed on that computer? Do you have index on that computer? Is there a anti virus running on that computer? If there is No on all three those questions, then it is your solution that you need to work on. If there is any Yes, you need to make sure you get all three No.
Hmm, well the records aren't that much. only couple of thousand records shouldn't slow down the find this much.
Regarding FM Server, it is a dedicated server, I have indexing running on fields but Unstored Calculation obvioulsy can't be indexed. Anti Virus is not the problem, because its only the search getting slower, rest of the operations are running okay.
I did not mean indexing on field, I mean is the computer running indexing on your computer. If so, then your database is also a part of that indexing and that might get you a corrupt database that might crash and are going to slow down your FMS. Anti-Virus will be a problem if it is search for virus on your live database. If so, then your files might get corrupted and crash.