Hi
on the one hand I'd like to reassure you and ease your concerns, but on the other I'd also take it seriously and show it to your Dr.
Without anything to make any judgement call (no picture) its impossible to say anything I would be inclined towards "its a pimple".
What I'll say is that for me, on the day I was to be released from hospital after surgery I bent over to pick up my shirt and a small jet of liquid shot out of the top of my wound. It was mostly clear with traces of old blood. I was kept in a few days longer waiting for the results of a swab and blood tests and was released. The wound to my experience with this never settled as nice as I'd come to expect (from the last 2), but as my memory is hazy that far back (and I didn't take notes) I assumed I was just healing differently because I was 20 years older.
When it first became 'obvious' that there was something wrong it was not "subtle" or (to my mind) unclear ... it stuck out (as we say in Australia) like prawns eyes.
If you have anything at this stage its likely to be propioniacnes bacteria, that's the well known (not to cardiac surgeons however) 'smouldering' bacteria in prosthetic surgery. If it develops to some thing serious (and by serious it looks like this)
started as what appeared to be an impression of the top bone of my sternum, within 2 days was like this
and by another 4 days like this
so if you have something more serious than a pimple you'll not have too long to wait to find out
Keep us posted, and if you feel inclined pop up a photo here
(*note: my photo's are on flickr and I past in the url here between bbcode image tags )
Best Wishes
you wish to bring this up to the Dr