I am sure other ppl can answer your question better than I but I had a similar problem (I thought) on the left side. My ENT felt it and told me it was part of my thyroid and it was supposed to be there, don't know if that is the case for you but FYI.
I hope someone else will chime in but I thought I had read that you are still being treated, tumors can continue to shrink for some time after you finish going for treatments. That is just something I remember reading so don't take it to the bank. If you are concerned call your oncologist and get in there early to discuss it, that is why they get paid the big bucks.