M.C.
when was your last period?
most people wouldn't show signs of pregnancy after 1 week, and if the ONLY time you have had unprotected sex recently was 8 days ago, then I would guess it is unlikely you would have pregnancy "symptoms" this early.
I have never been on the depo shot, but any type of hormone- birth control will change how your body naturally "acts" during periods, and these changes are most noticeable when you first go on it, or first come off of it. when I was on "the pill" I always had super light periods and almost no cramping, but without birth control my periods are heavier, longer, and I get more cramps. Also, my "natural periods" are more sporadic; rather than being always exactly 28 days apart (start to start), they can be a lot closer together or further apart and sometimes I have had "mini" periods in between.
If it has been more than four weeks since your last period... go ahead and buy a pregnancy test. Otherwise, wait until you have a missed period since chances are a test too early wont detect the pregnancy anyways. In the meantime, do yourself a favor and don't do anything stupid, like get really drunk... just in case.
Good Luck!
-M.