I'm sorry to hear your still waiting for the exchange. To give you some comparison, I had Mx/SLNB/LD flap recon with tissue expander in Dec 2014. The expansions were done between Feb & May 2015 and in June a date was set for my exchange op, which was carried out in Sept 2015. The reason It had to wait until Sept was due to me having holidays booked in July & Aug.
My next appt. is end of Oct to plan the nipple reconstruction.
I don't know if my timescale is the norm or not but my surgeon has always informed me what will happen and when. More importantly he has stuck to it, which has helped me plan for work etc.
Do you have a BCN you can call to get some answers or even ask to see your surgeon again.
Hope you get your exchange soon xx