Scared I could be pregnant?

katie
I've been on Depo since May 2014. After the first few shots I stopped having periods all together. I to this day don't have a period at all. Recently my stomach looks a little bigger and I noticed a blue vein on my breast that comes and goes. Also a week ago I had a bout of nausea. 
I'm very scared as im 17 years old. 
If I were pregnant Id have to choose an aborition, I've never had surgery before and this is all very frightening. Is there a chance im pregnant? If I don't have my period does that mean I can't ovulate? Thanks