My big cyst has turned tender/painful

[MyMorningHasBroken]

After approx ten years of absolutely no pain/infection, one biopsy (3 months ago benign) and ongoing growth my huge cyst has become tender and sore to touch with a stinging sensation at times.
Can't see any other signs of infection from the outside. It's been like this for a few weeks but hasn't done much else. (kind of waiting for a massive explosion :()
It's a large 3 x 3 inch one on my back. Should I take a' wait and see' approach?
I know it has a very thick wall as they really struggled to get the biopsy needle in so guessing it won't go easily after 10 years and there is no punctum.