I am quite amused with this post.
How far can you go with O-levels? Ask around. Read the papers. See
what kind of qualifications they are asking for.
With the current education structure, about 25% to 30% go to the
Uni of each cohort goes into Uni, another 40% or so goes to Poly,
and the rest have O-levels and below. So if you just have O-levels,
qualifications speaking, you're in the bottom 30% or so. How are
you going to compete?
You should be thankful that you have a diploma now. If you find
your job boring, then you should do part-time studies to upgrade
yourself, get a degree, find a better job.
Surely you don't want to be stuck in this job forever.