Theres a gp practice at Sonntagstrasse 1, right by S bahn Ostkreuz. Sorry i cant remember the name of it, but they have X-ray facilities and are sort of orthopaedic- oriented. And very nice, speak some English.
you need obviously E111 card (which will puzzle them entirely as it has no krankenkasse details on the back) and your passport, and as far as i can tell, they should know which German Krankenkasse to bill it to. Its Barmer, incidentally.
www.barmer.deAny further qs if i can help, pm me as my internet's a bit ropey at the moment so im not often on TT right now.