Could I be pregnant?

Well its been 5 months, the first 3 I didnt get my period but I assumed it was because of the plan b pill i had taken within the 72 hours. I took pregnancy test around the second month I didnt get my period, it was negative. I was convinced I was definitely not pregnant, but my stomach had been hurting, ive been getting bigger, and the two periods i have had have been different, a bit more painful, shorter. It might sound like a stupid question to some, but I dont know I have this feeling that something is going on, can someone please give me some peace of mind