What Causes Missed Periods And Pain In Lower Abdomen After A Surgical Abortion?

I had a surgical abortion on 8/10/2010(barely 6 weeks). I had light bleeding/spotting for 3 weeks. No abnormal cramping. I Have not had a period since the abortion(10 weeks now). I have excessive pain/pressure in my lower abdomen and pelvic area especially with a full bladder. I always feel pressure as if I have to urinate. Sometimes stabbing pains in my lower pelvic area(left and right side,separately). I have had excessive weight gain/bloat? The scale says 6#. Feels AND looks like 20# plus. My clothes no longer fit. I actually feel bigger every day. I am normally a size 2. Last week I bought a size 6 and this week it doesn't fit.

I took a digital pregnancy test, it was positive. I immediately took two non-digital tests that were negative. Could I still be pregnant? If not, what could be causing this?

Note: I was not able to make it back for a follow up due to distance