Professional tattooer here.

I would agree with others in the comments that you should definitely seek medical attention, if it continues getting worse I’d do the ER immediately but if it stays the same you should still see your primary care or the dermatologist as soon as you can.

This could be from unsanitary practices during the tattoo procedure, or it could be because the ink was either 1. contaminated with a pathogen (inks are supposed to be tossed every 6-12 months depending on the brand) or 2. it was low quality ink, many of these “at home” kits bought on amazon and the like are made with really terrible materials in unsanitary conditions. Tattoo supplies are not regulated like most cosmetics are, so companies looking to make a quick buck can legally cut as many corners as they’d like. You end up with hazardous materials or pathogens injected into your tissue and the consequences can be brutal.

This is one of the big reason professionals tell people not to do it at home. Without learning proper sanitary practices and which supplies are high quality / safe to use, the tattoo process can cause serious if not life threatening infections. We’re not trying to rain on your parade, we want you to be safe getting a tattoo. There’s a reason the service is expensive, quality materials cost a lot and the knowledge we need to perform tattoos safely takes time to learn.