it sounds pretty normal - your body is being stimulated to a much higher degree than it would be for normal ovulation. plus it's being forced to wake up from a drug induced menopause (the synarel) so it's going a little nuts from it all

mention it to your clinic, but it's not something to be overly concerned about. my breast always hurt while stimmin - and when going through full stim for ivf as opposed to the lower stim for IUI, it was a very different degree of pain