I think my daughter doubled in age overnight...

My daughter had her four month checkup/shots on Friday (so two days ago). She weighed in at 18.5lbs (thus officially doubling her birth weight) and 27 inches long! Later that day I noticed she was cutting her first TWO teeth (bottom centre)...the little white tips have broken the skin! Today, she is standing up with the aid of the couch...and maintained the pose for several minutes...

....what is happening?!?!?!