I had PRP with ACell injections on my scalp. The next day I woke up with a lump on the back of my ear? (photo)

In my opinion, the lump behind your ear is probably due to edema from the Acell procedure. 24 hours is very early for an reactive phenomenon from the foreign proteins in the Acell. If it resolves quickly, this will confirm the etiology. Please return to your provider for follow up care.PRPHAIRMD.COM 

I am not sure what the swelling behind your ear is about. I suggest you see your injector for a full examination. An appropriate follow up is going to be important to limit complications. 

It's difficult to tell from your pictures. I recommend following up with your Doctor for a formal evaluation. This could be your lymph node. For best results with hair growth,  I do prp with progesterone injections. I also have all my patients use viviscal, rogaine, and propecia when getting prp. See an expert. Best, Dr. Emer

Very hard to tell from the photograph. I think you should follow up with the provider who did the procedure. If the lump is fluctuation it could be accumulation of fluid in the area, although unlikely. If it is firm it could be a lymph node. 

Thank you for your question and posting your photo. I would recommend following up with the physician who did your PRP. Chances are it is a reactive lymph node but it should be examined to determine whether any intervention is indicated.I hope this was helpful - Dr. Moore.