Welcome to HCM.Blood clots
are common in women on birth control pills more than 2- 3 years. Back surgery also predisposes for vein blocks. In your case, I am suspecting local inflammation and swelling due to tattooing and not blood clots.
Blood clots or deep vein thrombosis
is a serious condition and has to be treated as an emergency.
I suggest you get in touch with a specialist for examination of your foot swelling to rule out infection.