Hey there. Congratulations on your transplant! I had a double lung and liver transplant 19 months ago and am doing great. I had a couple of run ins with rejection in the first 6 months so that might be what you are experiencing. I do not remember if I had any symptoms for mine. The doctors had found it when they did my routine bronchs. I can tell you though that SOB and lower O2 levels are two symptoms of rejection. If this is the case (and it is acute) they will have you on three days (normally anyway) of Solumedrol, which is not fun. I dreaded the three days of Solumedrol but it worked and the rejection went away. I now saturate at around 99%, my FEV1 is 94%, and I have no SOB.
I really hope that things go well for you. Let us know what happens!