Lipoma? Or not?

I recently discovered a fairly large lump just left of my belly button. My physician tells me that it is a lipoma and that she can remove it at her office. I haven't had any tests and it's causing a lot of discomfort and pain along with irregular bowels. I'm concerned about having it removed since there were not any tests done prior. I'm not sure if I should go ahead with the surgery or look into having some tests done to make sure that this is a lipoma.