How can I be sure?

I just took 4 different pregnancy tests and they all say positive but I can't get in to see my doctor till march 7, so until then how do I know for sure I am pregnant?  Also my period has always been irregular so it's hard to tell how far along I am. I guess I feel sure enough to at least tell my husband, but what about everyone else close to me?  Or even people like my instructor at the gym so she can give modifications?  Is that important?  I don't want to tell her before I tell my family but do I need to have modifications?  Thank you!