I also asked my doctor about the lump that appears above my belly button when i tense my stomach muscles as though to do a situp. She explained that hormones can also cause it, and it's not just caused by the baby getting large, but would like to refer me to a physiotherapist who can give me exercises to stop the split, which is called diastasis recti, from getting worse and maybe even repair it. I'm inferring from that it's not normal this early in the pregnancy, which is what i suspected anyway.
She also thinks the 15 week appointment with the Medical Clinic is to do with my thyroid. I'll bring in the results of my latest blood test with me when i go there.