Random bruise by bellybutton

So I don't think I did anything to get a bruise, and I normally don't bruise easy. But this morning when I took my shirt off, I noticed this bruise.

I'm 11 weeks pregnant, and my son is 7 months, so I'm only 7 months post op from a C-section. My doctor didn't seem concerned about that at all, but the last few days I've been having some soreness (mostly feels like muscle pain) and now I have a bruise a little above where the soreness is. I plan on talking to my doctor, and I plan on going to the ER if the bruise spreads. I'm just wondering what your thoughts are and if any of you got random bruises during pregnancy.