Everyones different matey, don't worry 
Does the SL routine not say what to do if you stall? Just drop the weight and go back up again? It may be a case of attacking the sticking point with what you can, eventually you should get 5 reps.
That or eat more
EDIT: Try above first

Does the SL routine not say what to do if you stall? Just drop the weight and go back up again? It may be a case of attacking the sticking point with what you can, eventually you should get 5 reps.
That or eat more

EDIT: Try above first