I keep a semi regular log of tds readings after RO and after DI, this can come in handy if you have tds problems
What size resin vessel are you using
What is the tds reading after RO as this might explain why your reading has gone up
Resin doesn't last forever
Even when I'm not using much water I try to empty the holding tank so I can leave the water running for longer, don't know why but my resin seems to perform better when it gets a longer run rather than short bursts
As for the speed I would check for blockages (unlikely, but won't hurt ) or it might be something simple like water pressure problems in your area