do we need to go to the er?

breast feeding mom
I am 99.5'% sure my baby has thrush. 
His dr isn't open till Monday. But they are on the inside white lesions and all over his tongue. Ftm. Should I take him to the er? Or wait till Monday and can someone fill me in on what Is thrush? Like does it hurt him? 
I had to hold him still to get a picture he is 7 weeks.