Possible Duplicate:
Proper usage of “since” and “from” with regard to duration of time
Is “since I’m” now an acceptable alternative to “since I was”?
With the Present Perfect (Progressive) "since" can be used when a reference point is indicated, e.g.:
I've been working here since last month.
Can I use "since 2 months ago" as a reference point, as in:
I've been working here since two months ago.