Couple of things that can cause the irritation is heat/sweat that rubs against the skin as the tattoo is actually scar tissue so can be come inflamed quite easily.

The other is some pigments have trace metal elements (quite rare but depends on the make) which can become inflamed as the body is trying to flush the foreign body from your system.

Again it could be non-tattooed related and be a allergic reaction to chemicals used in soaps, perfumes etc.

My advice is always apply an ice pack to any swelling for as long as you can stand and if you have anti-imflammatories (ibruprofen) or anti-histamines (health allowing) try them.

If it continues for more than 24 hours or starts to blister, discolour, red streaks or bruising etc get straight to a doctor.

Also that tattoo is very nice and it don’t suck. It is just a matter of artistic taste and frankly mine rocks 😉

Take Care
Matthew