I was unsuccessfully treated with strep throat and now have a bacterial upper respiratory tract infection. is this a complication?

Sure.: Once you have irritation from any disease and excess mucus is present, another bug can move it. Mucus is a germ magnet. It doesn't happen all the time, but it happens quite often. Usually appears 7-10 days after strep (new germs have to multiply enough to cause symptoms.) The antibiotics that help strep, won't prevent germs immune to it from moving right on in.