Floors of Bathroom Very Creaky
It is not unusual for the floors in older homes to creak some, but what you are describing sounds like there is some damage to the structure. Since it is the worst around the toilet, I am betting that there is a leak somewhere which is slowly rotting out the floor.

If you have access to the floor from underneath, look for dark stains on the wood around the toilet stack. Try poking around with a screwdriver to see if there are any soft spots. The floor most likely will need to be repaired, before the repairs are done, you should identify where the active leaks are so you won't have this problem in the future. It is most likely leaking from somewhere around the toilet. The wax seal may have failed, or it is dripping from above and making its way onto the floor.