Unsure of date of last period

I've been on the pill for a number of years now. I last had a period in January, but ran my pills together the months of February & March so that I would not have a period. On March 22nd I felt period pain and stopped my pill in the hope that I would menstruate but it did not come, despite having my normal period pain. On March 27th my husband & I had unprotected sex. It's now the 11th of April and I have yet to have a period. I've had some bad abdominal cramping the last week or so, and do have bouts of nausea which last for a few minutes only. Some light dizziness as well and tender breasts. However I do get tenderness when I'm expecting my period. My stomach is bloated and hard and I am constipated. I am unsure if this could be pregnancy or my hormones just out of wack cos I haven't had a normal period for 3 months almost. I did take a pregnancy test on April 8th and it came back negative. Can you please shed some light on this?