Ask your company. All these designations differ from 
Company to Company. There is nothing wrong in asking what 
your designation is.

Check what is written in your appointment letter if you 
have received any from your company OR ask for the same to 
the HR of your company

Hi, if you are testing any web portal OR doing something 
that is as same, then you are acting like a tester, as 
testing is a part of QA, but their is diffrence in QA 
engineer's task and QC engineer's tast. QA is mostly 
related to the standards e.g. CMMI levels, SIGMA levels 
ext; are they being followed properly OR not, are the 
document being prepared according to the TCl or not. As 
well on the other side tester is related to the Software 
testing tasks, preparing the Documents, practising diffrent 
type of testing on diffrent levels e.g. Function, 
regression, then smoke N sanity ext.
So as per my knowledge is concerned, i has provided you 
with best of it.