Get it checked out. I'm suspicious of all lumps and your doctor should be able to tell you if it's anything to be concerned about. If anything he/she could request it be looked at while you're getting an ultrasound.
I don't want to alarm you but I felt a lump in my abdomen when I was pregnant with DS. The lump kept getting pushed up until it was just under my rib cage. I had my dr. check it out and he said that pregnancy pushes things around and it was probably just one of my organs getting the squeeze. It was still there after I had my son so I got it checked again. The short of my really long story is it turned out to be cancer. I didn't get cancer from being pregnant, however the pregnancy hormones made the tumor grow quickly (I had surgery when my son was 7 months and have been cancer free since). It's not normal to have lumps as far as I know so I'd get it checked out.