Antibiotics...acne gets worse b4 it gets better ??

After years (10 to be precise) of battling with various medications
including two courses of Roaccutane which done me no good, I decided
to come off all medication/lotions and potions. A year later I was
almost 100% clear for about 8 months... a couple of months back the
spots started coming back..slowly but surely. Now my forehead is full
of them again,..new ones appear every single day. What caused this, i
dont have a clue!! I decided to go to the GP again. I was given
Doxycycline (50g daily) and Zineryt Topical (Erythromycin & Zinc).
I've been on these for 3 weeks now and things just seem to be getting
worse. Im even getting spots on my back...haven't see them there for
years!

When on Antibiotics, does acne get worse before it gets better? Or is
my condition just getting worse? And how long should I wait to see
results before I come off this medication?

Im just a bit sick of it all..i don't know what to try next.

Thanks guys
Sav