Could I be pregnant?

I'm 29 years old and already have a 4 year old.When I was pregnant with my little boy I took 3-4 urine test that come negative but just had that feeling that something is there.I find out I was pregnant after 2 months just because I still had my period.My period was pretty regular(5 day).Now after steroids for back pain and back surgery(over 1 year ago) my last 3 months can't  really say was regular.My belly looks huge, my period is 1-3 day.Took urine tests but all negative.Before my period come my breast is getting bigger(that didn't happen so much before) and last a couple of day.I'm thinking to take a blood test just to see if is something there and make sure I do the right choises in case I'm expecting.What u all think about it?