Growlithe not levelling

[dr007]

growlithe is gaining exp but exp bar is not moving
i even tried using only growlithe to train, he is killing everyone but still not levelling up

 

[Mike]

All poké in slow and erratic exp groups are caught with an exp total too low for their initial level;
They do earn exp, but need more exp than anticipated for their first level up,
and their blue exp bar will not display correctly until their total exp catches up to where it should be for their initial level
Bulbapedia page "experience" has a table showing total exp requirements for the six experience groups