Raised Tender Tattoo

I got a tattoo in july and it healed perfectly fine. However for the past 2 weeks it has been raised and tender(sensitive to the touch). I also get abit of cramping underneath it. The tattoo itself looks normal, but puffy. It isn't red or hot at all. I did scratch it about a month and a half ago with my finger nail, but it was just a little scratch, not deep or large at all and that seemed to heal fine too. Is it possible to have an infection underneath the tattoo which isnt visible or detectable? Could my skin have an allergy or be rejecting the tattoo? The artist told me to put a thin layer of polysporin on it for a while. It helps but its still not back to normal.
I also have swollen lymph nodes in each armpit and my groin. I had a physicial a month ago and that was all normal. Should I be concerned?

P.S. I don't need a lecture about tattoo risks etc. I went to a reputible place.