From what you say it sounds like your due for a refresh on stone. 1 razor for 4 months is right in the time frame for refresh though. I don't use pastes and maybe more time with the crox would do it. Euclid440 is my paste expert and he may be along soon with a more definite answer.
The starting sharp and losing it after a few passes makes me think more stropping but you been doing fine for months so ???