You know the storyline is in trouble when the writers revert to poop jokes like five year olds...
I know this is a favourite of many, and it broke my heart a bit to drop it because the cells really were fantastic and if they had their own show I'd love it! But unfortunately, the cells were never meant to be the main characters of this drama, it's a love story between two flesh and blood people and it isn't a very interesting one. We have misunderstanding after misunderstanding, an Evil Other Woman and of course, the famous poop humour. All these "delights" can take up half an episode, and that just makes the overly long episodes seem even longer.
No show can survive on only a cute gimmick, there has to be good writing involved. Sadly, the writers concentrated too much on good lines for the little cells, and the main couple was left with second hand scraps. And that's my cue to run far away from this drama.