grand get slow after using some days... topic

Guys I have a Galaxy Grand Duos, rooted, installed cm12 by pawitp, over i9082ddubnb1 basenand...

whenever I made a fresh install of cm12, it works preety well for upto 1 month, then it startet lagging, even after cleaning cache partition....

I also feel the same problem with my uncle's grand, stock unrooted with bng1 firmware...

any sollution to this

thanks in advanced...