I have tattoos and have never had that happen.
If it is green stuff coming out, it is probably infected.
Do you know if he used a clean needle?
You should probably go to a place like CareFirst or something and get that checked out
I found this, which seems relevant to your question.
What have you been using for your aftercare? If you are using any ointment, stop right now. If you have been using Neosporin, then that is probably the cause. and could be an allergic reaction, it can cause the color to come out in the spots where there were 'pimples'. Any petroleum products? Anything with Lanolin in it? Fragrance, dyes? Any of these could be the cause. You could have clogged the pores, not allowing the tattoo to breathe.
So, if you only have 1 pimple, you are probably o.k., but no matter, follow excellent aftercare no matter what it looks like. Keep washing 2 -3 times a day with antibacterial soap, pat with clean paper towels, air dry, apply a thin coat of Lubriderm unscented lotion, no sun, no soaking, no direct streams of water, no rubbing, no towels or cloths, keep in the air or covered with loose clothing, no sunblock until completely healed to skin, with hair growing, and it does not hurt when you bump it.
If it swells, looks infected, then go to a doctor. Try 600mg. (3 200mg. tablets ) ibuprofen every 6 hrs for 24hrs. (no longer without consulting a doctor) to minimize inflammation.
Your tat will go through many phases, don't panic, (peeling, redness, swelling, milky film over it, shiny,.. etc.) just care for it and wait, maybe 2 - 4 -6 weeks.
If color has come out due to any allergic reaction, have the artist do a touch up at this time, and start all over again with excellent aftercare. (you will be safe to use antibacterial soap and Lubriderm the whole time)
good luck, (and again, your tat is probably o.k., you just have to wait it out)
You need to see your doctor. You are describing an infection. It sounds like its getting worse. You probably will be prescribed antibiotics.